I am considering switching an existing Exim mailserver for a Cloudron instance.
One feature I need to maintain is a custom mail routing rule which allows mailbox addresses with an arbitrary prefix, designed to implement disposable addresses for use as casual log-ins, inspired by spamgourmet.org.
Is this possible with the default Cloudron mail service? Perhaps using some custom configuration, for instance, can SpamAssassin rules do this?
I'll explain the use-case in more detail briefly.
I might have a mailbox email@example.com, and an alias for this, firstname.lastname@example.org, which by itself doesn't accept mail, but will forward mail to email@example.com when prefixed with any arbitrary word (delimited by dot). For example, firstname.lastname@example.org, email@example.com and firstname.lastname@example.org would all forward to email@example.com by default, as well as any other prefixed address you could think of.
This allows unique email aliases like this to be invented off-the-cuff when creating a log in for a site requiring an email address to register a user account. These addresses can be disabled if and when they start attracting spam (perhaps because the site has been penetrated by malware, and the user data captured and redistributed in spammer databases).
Because they are unique, the addresses also tends to reveal the source of a breach, because the prefix indicates what it was used for originally.
Disabling an address is done by firstname.lastname@example.org sending an email to one of her aliases with the subject
!off, via an authorised connection to the SMTP server implementing the prefix aliases.
If switching to another implementation, the mechanism for managing these aliases could change, but I'd need the addresses to continue working, obviously.