The headers of messages sent from our email service usually contain an number which relates to the address the message is sent from and is used to track abuse of our mail service.
We don’t like to think that people would sign up and then use our service for sending messages they shouldn’t, but it does happen from time-to-time and we have to be able to find our which account is sending those messages.
In the outgoing headers we add a unique identification number (ID number) that relates to the email address that a message claims it is from.
If the email address matches a username or alias in our system we lookup the ID number of that address and add it to the headers. This appears in the following form for messages sent from the webmail and also via SMTP with an email program.
[Authenticated alias (123456)]
In messages sent from the webmail it is also contained in a special header in the form.
The alias ID is unique for each username or alias.
If an email address is used that isn’t an alias or username on the account the message is being sent from then to ensure we can still track which account the message was sent from we use the user ID (UID) number of the account that sent the message instead.
If you have any questions about this, please contact Runbox Support.