I found by testing that our e.email addresses support aliases like Gmail does, i.e use “+[alias]” after your username where [alias] is whatever plaintext alias you want to use.
However, if you be great if this was documented somewhere to explain what is permitted and what is not. e.g. can “_[alias]” also be used? What about “.” in the [alias]? Other special characters? Are subdomains supported, e.g. email@example.com?
Note I did further testing and subdomain aliasing and “_” aliases do not seem to work, they were returned to my test account. However, numbers and “.” in the alias work. I don’t know which other special characters are supported though.
I haven’t had chance to check if it can also file the emails into folders according to the alias used, but this would be a great feature. My main use case at the moment is I add an alias to my main username which identifies the company to whom I am giving this address so I can in future tell who they give it to. I know that subaddressing is easy to bypass, as they can just delete the +[alias] part, but it is at least helpful.
The NextCloud Mail documentation on this is terrible/non-existent as far as I can tell from my research. /e/ needs to have good information on things like this to meet the objective of being for everyone, not only the techies.
It would also be nice to know if /e/ intends to add other aliasing possibilities, like Hotmail/Outlook does, where completely new names can be associated with a single account. This can also prove useful where normal subaddressing is not sufficient.