Why are my emails not being delivered?
Under certain circumstances, it may be the case that individual emails cannot be delivered. The reasons for this are highly varied, but in all cases you will receive a bounce email (notification that message could not be delivered).
This email always contains the reason for refusal of delivery. The reasons for refusal are standardized according to various guidelines. In most cases, the refusal is sent by the email server of the email recipient.
We have listed frequent reasons for refusal and what they mean in the following:
| RFC | general reason for refusal | What is the cause? | What is the solution? |
| mailbox full | Recipient's inbox is full | The recipient needs to free up storage space for emails in his inbox. | |
| Refused by local policy. No SPAM please! | Your email violates the filter and/or spam rules of the respective recipient. | Please check if your email contains content which could be identified as spam. | |
| B-URL or B-Text | Your email contains text or a URL which has been declared as spam. | Where applicable, remove links or negative terms. This also applies to corresponding content in signatures. | |
| RFC | error in address | What is the cause? | What is the solution? |
| 550 | sorry, no mailbox here by that name | Email address of recipient does not exist | Check if the email address is written correctly and ensure that the email address still exists. |
| 550 | recipient e-mail address unknown | Recipient email address is unknown | Check if the email address is written correctly and ensure that the email address still exists. |
| 550 5.1.1 | <example@desiredname.de>... User unknown | User/inbox does not exist | Check if the email address is written correctly and ensure that the email address still exists. |
| 550 | Forbidden domain 'xxx' in Envelope-From (B-EFROM-STRATO) | An attempt is made to send an e-mail using a domain in Envelope From (aka. "Return Address") that belongs to Strato AG. You are not allowed to use this address. This would mean that all non-delivery notifications (aka. "Bounces") would arrive in a mailbox at Strato AG instead of yours. | When you send a new e-mail: Use your own e-mail address in the Envelope From and in the "From:" or "Sender:" header of the new e-mail. If you want to read an already received e-mail from your mailbox and "forward" it as a new e-mail: Use your own e-mail address in the Envelope From. Leave the original email completely unchanged. Also, do not change neither the subject line by adding words like "Fwd:" in front of it, nor the "From:" header. Otherwise, any DKIM signatures in the e-mail will become invalid and there is a risk that this e-mail will be rejected by the receiving e-mail server. A better way to forward e-mails is to forward them using a forwarding filter rule. Such a filter rule can be set up in the Strato Webmailer or in the E-mail Administration section in the Strato Customer Login. The safest way to forward e-mails, so it can survive even DMARC, is to create a new e-mail, attach the original e-mail as an ATTACHMENT to the new e-mail, and send this new e-mail with your own e-mail address in both, the EnvelopeFrom and the "From:" header. Always use the very same e-mail address in Envelope From and "From:" header which you are using in SMTP authentication. Otherwise, this new E-Mail will fail a DMARC alignment check and could, therefore, be rejected by the receiving e-mail server. |
| RFC | Filter | What is the cause? | What is the solution? |
| 550 | relay not permitted | Access not permitted; login error | Check the login details (email address and email password) for typos. |
| 550 | Mail was identified as spam | Your message was recognized as spam | Please check whether your email contains content which could be identified as spam. |
| 554 | Relay access denied | Authentication failed | Email server of recipient is not configured. The recipient should check his DNS settings. |
| RFC | temporary issues | What is the cause? | What is the solution? |
| 451 | Temporary local problem - please try later | temporary delivery problem | Send the email again at a later point in time. |
Note: Temporary issues will not result in an immediate reply with a bounce email, as it can be assumed that it will be possible to deliver the email at a later point in time. In this case, the email server will keep the emails in the queue and attempt to deliver them periodically. It is only when the email has been in the queue for too long that the system will need to send out a bounce email and delete the email from the queue.