Information on the delivery of e-mails

If you receive a message that your e-mail is undeliverable, there may be various reasons for this. We have summarized the most important questions and answers on this topic below.

There are various reasons why e-mails are not delivered:

  • The maximum size has been exceeded (e-mail including header, mail text and attachments).
    • E-mails up to a size of 99.6 MB are accepted at the mail gateway.
    • The limit for employees' groupware mailboxes is 50 MB.
    • The limit for student mailboxes is 20 MB.
  • The recipient's mailbox is full.
  • The e-mail contains attachments that have been classified as security-critical by the HRZ and InfoSec.
    • Encrypted attachments that cannot be scanned by the virus scanner.
    • Media types (mimetype) and file extensions classified as problematic, e.g. outdated Microsoft file formats such as *.doc, *.xls, *.ppt. (A complete list of blocked formats is not published here for security reasons).
  • Other reasons why e-mails cannot be delivered:
    • The e-mail is classified as problematic by centrally deployed virus and spam checkers due to its content or the sender address.
    • The recipient address does not exist. (Note: In the case of decentrally operated e-mail systems, this can also mean that the e-mail address was created locally but not reported to the HRZ).
    • It is a purely internal target address, but the e-mail comes from outside TU Darmstadt.
    • The address is on a blacklist.

If an e-mail cannot be delivered, it is either

  • rejected directly with an error message
  • forwarded and delivered at a later date

or

  • sent back to the sender address with a message after five days of undeliverability.

If an e-mail is rejected for security reasons, the HRZ will be able to trace this. Please report specific cases which need to be clarified to the HRZ as soon as possible (within three days) so that general cases can be identified.

The sender will be informed of the rejection by e-mail.

If an e-mail is rejected due to an unaccepted file format, the recipient will also receive an e-mail with the following content in future:

  • sender
  • date and time when the e-mail was sent
  • file name, if available

Please: If the receiving address does not exist, this message cannot be sent.

No loss of e-mails is to be expected in the event of a system failure. E-mails will be delivered as soon as the system is available again.