When the Postfix QMQP server receives mail with an envelope
sender address of the form:
Postfix generates sender addresses
"[email protected]", using "-=" as the VERP
delimiters because qmail/ezmlm expect this.
More generally, a sender address of "[email protected]@"
requests VERP style delivery with sender addresses of the form
"[email protected]". However, Postfix allows only
VERP delimiters that are specified with the
parameter. In particular, the "=" delimiter is required for qmail
compatibility (see the qmail addresses(5) manual page for details).