RFCs don't define any meaning to '+' as described in this thread, except that local part of the address should be interpreted locally (usually by MDA), and preserved unmodified during message transfer.

There's no + aliasing in the specs. There's no interpretation defined for local part of email address.

Oh, yes. I meant "+" is an acceptable character to use in the local part of an email address, as per the RFC. I see now where the misunderstanding lies.