[kelnos]

Yes. Any email service should allow it, as it's standardized and very old.

However, some services that you sign up for might reject email addresses with + signs in them.

With Gmail, one thing you can do is insert a period anywhere you want in your email address. For some reason they decided to ignore that character when matching incoming email to an account. That behavior isn't standard, but services you sign up for should never have a problem with it.

[hk__2]

> Yes. Any email service should allow it, as it's standardized and very old.

As far as I know it’s not standardized at all; it’s not in the SMTP spec. It’s actually annoying that some people assume this is standard because they can break functionality, like assuming foo+bar@ is the same person as foo+qux@ when it’s not guaranteed to be.

[stonogo]

It's not in the SMTP spec because SMTP doesn't need to know about it. Your objection is correct but in fact that's the desireable behavior -- senders can't assume that foo+bar and foo+qux are the same person. If they could make that assumption, subaddressing would be defeated as a useful filter signal. As it is, it's not just plus signs -- qmail has been using '-' as the subadress separator for decades.

Subaddressing is standardized in RFC 5233 as a filtering signal.