Common Mail Service Errors

If the letter was not delivered to the recipient, then he will be assigned one of the following statuses:

• Canceled/Forbidden — if sending a message is limited by the internal functionality of GetCourse. For example, a user is banned, unsubscribed from a mailing category, or no longer meets the mailing criteria. 
• Error — if the letter was sent to the user, but for some reason could not be accepted by his mailbox. At the same time, the mail server returns the error text to us, having analyzed which we can understand the reason for the non-delivery of the letter.

This article will present examples of error texts that can be returned by the mail server, as well as their description.

All errors in the article are divided into the following categories:

• Invalid user email address
• Errors in the domain name or domain configuration
• User mailbox is overflowed or blocked
• Mailing got into Spam on mail service end
• Graylisting errors (gray lists)
• Incorrect mail configuration errors
• An IP address from which emails are sent is blacklisted

To find the meaning of the returned error in the article:

1. Copy the error from the mailing.

2. Open this article in your browser and paste the error value into the page search bar (Ctrl+F).

Invalid user email address

The letter cannot be delivered to a non-existent address:

• Mailbox does not exist. We do not relay
• No such user! 
• Unknown user
• Recipient address rejected: User unknown in local recipient table
• The email account that you tried to reach does not exist
• sorry, no mailbox here by that name
• no mailbox by that name is currently available
• Requested action not taken: mailbox unavailable 
• Message was not accepted — invalid mailbox
• Bad recipient address syntax
• Bad address mailbox syntax
• No correct recipients
• We do not relay without RFC2554 authentication

Recommendations:

1. Try to contact the recipient using an alternative method of communication to find out the correct email address.

2. Change the user email to the correct one. 

To change email, click "Autorization" — "Change email".

Errors in the domain name or domain configuration

• MX lookup failed for [...] 

This error indicates problems with the MX record of the domain to which the message was sent, or for some reason it was not possible to check its MX record. Perhaps, during registration, the user specified an incorrect mail address.

If, when sending a letter, it is not possible to contact the mail server, the message will return with one of the following errors:

• Called MAIL FROM without being connected
• SMTP connect() failed
• RCPT TO command failed 

Causes and Recommendations:

• Typos in email addresses
• Corporate domain restrictions
• General recommendations for emails database

Typos in email addresses

While registering, a user can make a typo in their email address. Mailings cannot reach such adresses. Most commоn typos are:

• gnail.com or gmail.con instead of gmail.com
• yahoo.con or yaho.com instead of yahoo.com

Recommendations:

We recommend to periodically check the database on incorrect email addresses and change them to the correct ones.

Attention! Email address is correct if it is confirmed. It means that the greater number of users confirmed their email, the fewer errors in addresses there will be when sending mailings to “Addresses that have given their consent to receive emails”. And the deliverability is higher.

Corporate domain restrictions

Corporate mailboxes are mailboxes with domains belonging to corporations, universities, stores, government enterprises, and intended only for their employees.

Corporate mailboxes most often have their own mail servers, individual spam filters or other settings that can affect the deliverability.

Recommendations:

• Contact corporate domain owners providing an example of the error to clarify why your mailings are not accepted.
• If there are not many users with such a corporate domain, then the most optimal solution would be to ask the user for an alternative email on a more popular service (gmail.com, yahoo.com, etc) and change email in the user’s profile.

General recommendations for emails database

We recommend to use email addresses registered on the most popular mail services for security reasons and for higher deliverability.

Important! To reduce the risk of your mailings being classified as spam, send mailings to "Addresses that have given their consent to receive emails”. Such users have provided consent to receive mailings, and their addresses definitely do not contain typos. Therefore, it is important not only to collect a database of email addresses, but also to confirm them using DOI letter.

We also do not recommend using temporary mailboxes as email addresses. A temporary mailbox is a mailbox that does not require registration and allows you to receive emails that will be deleted after a certain period of time. For example, @yopmail.com or @maildrop.cc. 

As a rule, such mailboxes have a number of restrictions. For example, they may not support the html version of the mailing or may not be perceived as reliable recipients as they do not belong to real users. Sending mailings to them can affect the sender's reputation, and, consequently, reduce the deliverability of your messages.

We recommend to unsubscribe from mailings or delete users with temporary email addresses.

User mailbox is overflowed or blocked

• Mailbox size limit exceeded
• Mailbox size exceeded
• User is overquota
• User quota exceeded
• The email account that you tried to reach is over quota
• The recipient's inbox is out of storage space

Some services block mailboxes after a period of non-use. If you try to send a letter to such a mailing address, then the following errors will return:

• Mailbox [...] is locked due to inactivity for more than [...] months
• Аccess to this account (user) [...] is disabled
• Mailbox is disabled

Causes:

Such errors mean that there is no space in the recipient's mailbox to receive your message. Most often this happens because the recipient rarely uses the mailbox and it is filled over with mailings.. Such emails can also become spam traps, sending mailing to which leads to a significant deterioration in the reputation of the sender.

Recommendations:

Try to contact the recipient using alternative methods of communication and report the problem.  If the recipient cannot be reached, you can unsubscribe them from receiving mailings. We recommend periodically unsubscribe from mailings the list of users who do not read your messages.

Getting into SPAM on the mail service

If the message is rejected by the spam filter of the mail service, the following errors are returned in the message:

• IP [...] Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been temporarily rate limited — this error is returned by the Gmail if Google suspects that too many suspicious emails (spam) are being sent from the sender’s IP address. In this case, Google turns on a temporary limit on the number of receiving emails.
• Message rejected under suspicion of SPAM
• Client host [...] blocked using spamsource.mail.yandex.net
• Blocked by spam statistics
• 550 spam message discarded/rejected

Causes:

Sending mailings from your account, the recommendations for high deliverability most likely were not followed. For example, the sending domain was not warmed up or mailings were sent to a user base that did not give their consent to receive them.

Recommendations: 

Depending on which mail service your mailing was tagged as Spam, you can use one of our instructions to get out of spam:

• How to get out of spam on Gmail?
  
• How to get out of spam on iCloud?
  
• How to get out of spam on Microsoft?
  
• How to get out of spam on Yahoo?

Grayling errors (gray lists):

Graylisting is a way to automatically block spam mailings. The principle is: if the receiving mailing seems to be suspicious to the mail service, then it may not accept the mailing and ask you to resend the message later. In this case, the following errors may return:

• Greylisting in action, please come back later
• Greylisted, try again after some time
• Greylisted, try again in 180 seconds
• Sorry, the service is currently unavailable. Please come back later
• Temporary local problem — please try later
• Try again later

Recommendations:

GetCourse platform recognizes a similar request and automatically forwards the message later. Spammer software in such cases usually does not try to do this, and their messages do not reach.

However, If a mailing is returned with an error after 5 attempts to resend, the system records the error text and makes no more attempts to resend. In this case, the mailing can be resent manually after a while.

Incorrect mail configuration errors

• non-local sender verification failed 

Typically, such an error is returned by the Gmail or Mail.ru mail service.
If this error occurs, you need to check the correctness of SPF, DKIM and MX in the DNS zone of the domain from which the mailing is sent.

• Can’t verify [...] sender. Check your DNS configuration. 

If this error occurs, you must verify the correctness of SPF and DKIM in the DNS zone of the domain from which the mail is being sent.

• sender domain SPF exact match mandatory for IP [...]

Error in the SPF record of the domain from which the message is being sent. The SPF record may be incorrect or several SPF records may be present.

• This message was not accepted due to domain [...] owner DMARC policy (RFC 7489)

The message was blocked due to the strict DMARC mail service policy. You can implement DMARC, click here for more info.

IP address is blacklisted

If the IP address the mailing are sent from is blacklisted, the mail service returns errors:

• rejected because IP[...] is in a blacklist-dns at [...]
• Access denied, banned sending IP [...]
• Connection closed. IP [...] is listed in Blacklist
• [E-mail] blacklisted by [...]

If you receive such errors, please contact our Technical Support for further advice.