Imap and spam filter training query

[#1]

The google solution isn't (sic. a solution) if you look at it critically. The primary mail address is there in plain text (in the plain-text SMTP headers). The stuff before the  '+' character can be easily removed. The primary gmail address could be construed/argued as being 'personally identifiable'.

Perhaps there's more, as the headers returned from Plusnet servers in NDR's are very obviously edited/redacted versions.

[#2]

Having read your response twice I discern possible confusion of purpose here. There are two considerations here in using an alias (or creating a faux catchall).

1. Simply to facilitate an unlimited number of aliases without needing to do so explicitly, do as to give individual organisations unique email addresses.

2. To keep hidden one’ real email address.

Depending on how implemented aliases can do the above to a greater or lesser extent. Gmail being Google expect it to be to the lesser extent - full disclosure of the real email address without the bother of digging into message headers.

[#3]

"Gmail being Google expect it to be to the lesser extent"

Yes. Which is why I previously asked another contributor as to when Google implemented their version. Do you know? I was unaware that they had gone down this chosen path.

You may or may not know; I don't.

Is it related to the various problems of getting e-mails to g-mail accounts? I dunno, but perhaps having a date on when Google implemented their version of an alias might be useful in excluding them (or not) from the problems of e-mailing g-mail accounts. Putting a date (even a rough date) to the start of a problem is part of troubleshooting methodology (or part of change control procedures). The 'problem' for me started some time (let's say at least six months ago) before I popped up here. And the problem (as I see it) is not restricted to mailing g-mail accounts.

First 'odd' NDR that I still have stored was received back to November 2021.

What problems did PN have with e-mail back then? That's a start point,.