mbox.server272.com

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:31:51:c9:59:5e:a3:5a:7b:ee:23:9d:f1:7e:55:5f:88:6d was issued on by Let's Encrypt.

With 3 subject alternative names this certificate can be used to secure multiple fqdn's. This certificate has already expired and will cause a warning or error message in the browser it's still listed on this site to allow you to look back on previously issued certificates. If we have found any compliance issues with this certificate they will be shown below. I hope this certificate review is providing you the detailed information in a simple form you where looking for.


We have idenified some issues with this certificate:
  • Subscriber Certificate: commonName is deprecated. (BRs: 7.1.4.2.2)

Certificate Subject

CN=mbox.server272.com

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:31:51:c9:59:5e:a3:5a:7b:ee:23:9d:f1:7e:55:5f:88:6d
Serial Number (int): 278119406706366325782143726256722674681965
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: 99:ef:1f:52:aa:50:65:c4:28:a1:aa:c5:78:2c:d5:c1:05:62:18:84
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): d7:9b:1e:88:bd:37:96:eb:37:81:8f:24:c4:ea:fc:72:c4:71:d8:46
Fingerprint (sha256): 4a:bc:a2:97:73:dd:b8:db:e5:f0:ee:20:fa:0f:26:02:b6:7c:98:c0:64:9c:64:dc:73:4e:24:7d:b4:c6:69:81

Issuing Certificate URL: http://cert.int-x3.letsencrypt.org/

Revocation information

OCSP Server: http://ocsp.int-x3.letsencrypt.org

Check the revocation status for certificate mbox.server272.com

3

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for mbox.server272.com

Public Key Algorithm

RSA

Key Size

2048

Signature Algorithm

SHA256 with RSA

Key Usage

Digital Signature
Key Encipherment

Extended Key Usages

Server Authentication
Client Authentication

Extensions

8 extensions
No unhandled critical extensions

CA Certificate

This is not a CA certificate

Subject Alternative Names

mailbox.server272.com
mbox.server272.com
webmail.server272.com

Other certificates including the domain name server272.com

(limited to 100 certificates)
cp.server272.com
server-side-caching.server272.com
cp.server272.com
admin.server272.com
server272.com
mbox.server272.com
server272.com
catchall-server-default.server272.com
mbox.server272.com
server272.com
cp.server272.com
server272.com
autodiscover.server272.com
mbox.server272.com
autoconfig.server272.com
cp.server272.com
www.server272.com
www.server272.com
www.server272.com
mbox.server272.com
catchall-server-default.server272.com
rsapi.server272.com
rsapi.server272.com
cgi-sys.server272.com
cgi-sys.server272.com
builder.server272.com
www.server272.com
autoconfig.server272.com
cgi-sys.server272.com
mbox.server272.com
catchall-server-default.server272.com
cgi-sys.server272.com
mysql5-admin.server272.com
cgi-sys.server272.com
cp.server272.com
cgi-sys.server272.com
mysql5-admin.server272.com
catchall-server-default.server272.com
server272.com
mbox.server272.com
abuse.server272.com
autodiscover.server272.com
*.server272.com
autoconfig.server272.com
catchall-server-default.server272.com
cgi-sys.server272.com
catchall-server-default.server272.com
server272.com
www.server272.com
mbox.server272.com
mbox.server272.com
cp.server272.com
cp.server272.com
cgi-sys.server272.com
mbox.server272.com
cp.server272.com
cgi-sys.server272.com
mysql5-admin.server272.com
cgi-sys.server272.com
builder.server272.com
www.server272.com
cgi-sys.server272.com
builder.server272.com
cp.server272.com
cgi-sys.server272.com
cp.server272.com
cgi-sys.server272.com
newmail.server272.com
cgi-sys.server272.com
autodiscover.server272.com
cgi-sys.server272.com
server272.com
mbox.server272.com
cgi-sys.server272.com
appinstall.server272.com
mbox.server272.com
cp.server272.com
catchall-server-default.server272.com
www.server272.com
catchall-server-default.server272.com
cp.server272.com
mbox.server272.com
mbox.server272.com
cp.server272.com
server272.com
catchall-server-default.server272.com
catchall-server-default.server272.com
abuse.server272.com
socialsync.server272.com
mbox.server272.com
catchall-server-default.server272.com
mbox.server272.com
server-side-caching.server272.com
*.server272.com
mbox.server272.com
cp.server272.com
server272.com
catchall-server-default.server272.com
www.server272.com
www.server272.com

Certificate

The complete raw certificate details for mbox.server272.com in PEM and ASN.1 format.

Certificate (PEM)

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Public Key (PEM)

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA2/SOh2Le/Krk4mNbUoic
9kRAATN4IEvT0gq7sx9VHtj5y/wGBOOGtMH2aU30ipIcqQ5ze7QfgRu/8N4kYiJ9
LIANaFyeEO7CWcfOm7eNSDx25mhVUutJ0qPpH/FAGcCLgJUmxAl5fzWhGkv1p/QX
DhyF+48m7CsuM9c8VlLfSCjHR1BIDp2dRP9deSfb/VTFWF1xoc1gzdrifGZ3gF2H
Ym2v+TKoCXTMeG5P8BUHbglN6DhFYPRsjfe+m/v5qe/SUpYRpzIwdPBdvBg7A/MP
Occ/gnSqr1XJfSF834r1yzh83qryo8u2jRJfp/o8i5c8NXMkRs7AENXSwHBU1Fbb
VwIDAQAB
-----END PUBLIC KEY-----

ASN.1 decoded

 [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . [c:2|t:0|true] OtherName 
 . . . . . . . . . . . . [c:0|t:2|false] INTEGER 2
 . . . . . . . . [c:0|t:2|false] INTEGER 278119406706366325782143726256722674681965
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.11 (sha256WithRSAEncryption)
 . . . . . . . . . . . . [c:0|t:5|false] NULL 
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.6 (countryName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'US'
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.10 (organizationName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Let's Encrypt'
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.3 (commonName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Let's Encrypt Authority X3'
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2018-03-25 07:24:06 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2018-06-23 07:24:06 +0000 UTC
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.3 (commonName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'mbox.server272.com'
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.1 (rsaEncryption)
 . . . . . . . . . . . . . . . . [c:0|t:5|false] NULL 
 . . . . . . . . . . . . [c:0|t:3|false] BIT STRING (2160 bits)
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:2|false] INTEGER 27766784217286929841674061799285572454373885910848877871888742525193237509262130775832213039511008296921962704476197957407060656779073664219497972196217663880075696425487329555140972041256541701978429949123471524974876150394506303930681343078760100128581062929933110895873517258120059838749439640552183399138208236888083301377762981545520055177752381303134265750663803683336642349420217470916036498131129096252559704139627094926285975599638882370543458321185220388870342058433933949221920590736911602273871405226331631132385043552211646904782528098468538325453132055927633445179837909752866300983021108538147608124247
 . . . . . . . . . . . . . . . . . . . . [c:0|t:2|false] INTEGER 65537

 . . . . . . . . [c:2|t:3|true] ORAddress 
 . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.15 (keyUsage)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:1|false] BOOLEAN true
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (4 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:3|false] BIT STRING (3 bits)
							05a0
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.37 (extKeyUsage)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (22 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.3.1 (serverAuth)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.3.2 (clientAuth)
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.19 (basicConstraints)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:1|false] BOOLEAN true
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (2 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.14 (subjectKeyIdentifier)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (22 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (20 bytes)
							99ef1f52aa5065c428a1aac5782cd5c105621884
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.35 (authorityKeyIdentifier)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (24 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:0|false] OtherName a84a6a63047dddbae6d139b7a64565eff3a8eca1
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.1.1 (authorityInfoAccess)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (99 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.48.1 (ocsp)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:6|false] IA5String 'http://ocsp.int-x3.letsencrypt.org'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.48.2 (caIssuers)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:6|false] IA5String 'http://cert.int-x3.letsencrypt.org/'
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.17 (subjectAltName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (68 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'mailbox.server272.com'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'mbox.server272.com'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'webmail.server272.com'
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.32 (certificatePolicies)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (246 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.23.140.1.2.1 (Domain Validation Certificates Policy)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.4.1.44947.1.1.1
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.2.1 (cps)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:22|false] IA5String 'http://cps.letsencrypt.org'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.2.2 (unotice)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:12|false] UTF8String 'This Certificate may only be relied upon by Relying Parties and only in accordance with the Certificate Policy found at https://letsencrypt.org/repository/'
 . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.11 (sha256WithRSAEncryption)
 . . . . . . . . [c:0|t:5|false] NULL 
 . . . . [c:0|t:3|false] BIT STRING (2048 bits)
		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