Best Practices Top SMTP Error Messages – June 2016 By Ken Simpson | 5 minute read In 2012, we posted a list of the world’s most popular SMTP response codes. We are now pleased to present an update to the list. Using a slightly updated script, we Processed email delivery logs from the MailChannels Cloud SMTP relay service; Picked up all the SMTP response messages representing permanent delivery failures; Did a bit of string cleaning to remove serial numbers and other random-looking identifiers; and, Associated each log line with the organization that generated the error. Here are the top rejection messages (organized by the network that generates the error) Organization Response Code Meaning GoDaddy (secureserver.net) 550 5.1.0 23.83.x.y is not allowed to send from <example.com> per it’s SPF Record. Please inspect your SPF settings, and try again. IB508 <http://x.co/srbounce> The message was rejected because the sender domain (example.com) does not authorize the sending IP address in its SPF record. 552 5.2.0 9qos1t0… – 9qos1t0… This message has been rejected due to content judged to be spam by the internet community IB212 – If you feel this is in error, please submit a request using the following page. <https://checkspam.secureserver.net/?sid=9qos1t0…> GoDaddy’s spam filter thinks the message is spam. By clicking on the provided link, you can report the block as a false positive. AT&T (prodigy.net) 553 5.3.0 alph135 DNSBL:ATTRBL 521< 23.83.x.y >_is_blocked.__For_information_see_http://att.net/blocks AT&T’s spam filter has blocked your IP address. You can fill in a form provided by AT&T to request that your IP address be de-listed. Yahoo (yahoo.com) 554 delivery error: dd This user doesn’t have a yahoo.com account (email@example.com)  – mta1012.mail.gq1.yahoo.com The email address you’re trying to send email to does not exist. 554 delivery error: dd Sorry your message firstname.lastname@example.org cannot be delivered. This account has been disabled or discontinued [#102]. – mta1496.mail.bf1.yahoo.com The email address you’re trying to send to has been disabled or discontinued. 554 5.7.9 Message not accepted for policy reasons. Seehttps://help.yahoo.com/kb/postmaster/SLN7253.html Yahoo! has rejected your message for some other reason. 554 delivery error: dd This account has been temporarily suspended. Please try again later. – mta1102.mail.ir2.yahoo.com Yahoo has temporarily disabled email for the recipient you are trying to reach. This may happen if an email recipient receives a great deal of spam. Endurance International Group (eigbox.net) 550 <> Sender rejected. A bounce generated by your mail server has been rejected by the receiving server to which the bounce was addressed. Google (1e100.net) 550 5.7.1 Unauthenticated email from yahoo.co.in is not accepted due to domain’s 550-5.7.1 DMARC policy. Please contact administrator of yahoo.co.in domain if 550-5.7.1 this was a legitimate mail. Please visit 550-5.7.1 https://support.google.com/mail/answer/2451690 to learn about DMARC 550 5.7.1 initiative. s140si61565….111 – gsmtp Google’s mail server has rejected your message because the domain of the sender address (yahoo.co.in in this example) has a DMARC policy that you have somehow violated. DMARC enables domain owners to control how email from their domain may be sent. For more information, visit the link provided by Google. 552 5.7.0 This message was blocked because its content presents a potential 552-5.7.0 security issue. Please visit 552-5.7.0 https://support.google.com/mail/answer/6590to review our message 552 5.7.0 content and attachment content guidelines. c133si5731….145 – gsmtp Google’s mail server has rejected the message because it contains a file attachment that is of a “high risk” type. At present, Google prohibits the following types of attachments: .ADE, .ADP, .BAT, .CHM, .CMD, .COM, .CPL, .EXE, .HTA, .INS, .ISP, .JAR, .JSE, .LIB, .LNK, .MDE, .MSC, .MSP, .MST, .PIF, .SCR, .SCT, .SHB, .SYS, .VB, .VBE, .VBS, .VXD, .WSC, .WSF, .WSH 552 5.2.3 Your message exceeded Google’s message size limits. Please visit 552-5.2.3 https://support.google.com/mail/answer/6584#limit to view our size 552 5.2.3 guidelines. 198si450….22 – gsmtp Google does not accept attachments that are larger than 25MB in size. In some situations, smaller attachments may also be rejected. 550 5.7.1 [23.83.x.y 7] Our system has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please visit 550 5.7.1 https://support.google.com/mail/answer/188131for more information. x8si4242….230 – gsmtp Google’s spam filter has determined your message is spam, and has decided to reject it rather than put it in the recipient’s spam folder. 550 5.7.1 [126.96.36.199 11] Our system has detected that this message is 550-5.7.1 not RFC 5322 compliant. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please review 550 5.7.1 RFC 5322 specifications for more information. vw4si4702….180 – gsmtp Google blocks messages which are not strictly compliant with the RFC 5322 message format. 550 5.7.1 Please update the address to @example.com and try again. – gcdp j9si4733….36 – gsmtp The recipient you’re trying to reach has moved to a new domain. To fix this problem, you need to update the recipient address to use the new domain suggested (in this example, “example.com”). Microsoft (outlook.com, hotmail.com) 550 5.7.0 (COL004-MC2F47) Message could not be delivered. Please ensure the message is RFC 5322 compliant. Microsoft insists that your message be fully compliant with the RFC 5322 message format. 550 5.7.0 (BAY004-MC5F13) Unfortunately, messages from (23.83.x.y) on behalf of (example.com) could not be delivered due to domain owner policy restrictions. Your message was rejected because the sender’s domain name (e.g. example.com) does not permit delivering email from your mail server. Use the SPF record testing tool to find out why.