[mazambazz]

It depends on the underlying email server. But strictly speaking, the "+" is a valid identifier, and "[e-mail]" is a completely different address than "[e-mail]".

It just so happens that email servers tend to recognize the usage of "+" as a "tag" and route incoming mail using the tag to the root email that precedes the plus and tag.

But, as the sender, you cannot assume that this is always the behavior. You must assume that those are two different emails.

[sizzle]

I use periods and they work fine like for [e-mail] or [e-mail] which surprisingly resolves to my main email and I’ll block spam from any sender spamming that period address. Anyone know why this works?

[purkka]

This is a Gmail-specific feature. I'd guess it's there for user convenience and some protection against typos (accidental or malicious).

https://support.google.com/mail/answer/7436150?hl=en

[jpollock]

As a sender, that's entirely true. As a flag to identify correlated emails and accounts, it can be a very useful assumption to make.