what causes "Address verification in progress;" followed by status=deliverable (250 ok deliver to alternate)

[Larry Vaden [Permanent Link]]

Thanks for your help in advance.

Situation: trying to bring up a postfix box to act as inbound relay to
protect WinDoze box running several small domains;  using
reject_unverified_recipient as last line in
smtpd_recipient_restrictions.

What causes

NOQUEUE: reject: RCPT from host.example.org[nnn.nn.nn.n]: 450 4.1.1
<nosuchemailaddress AT example DOT com>: Recipient address rejected:
unverified address: Address verification in progress;

particularly the "Address verification in progress;" part?

20 to 30 seconds later there's another log entry:

postfix/smtp[3575]: 9D34D213C035: to=<nosuchemailaddress AT example DOT com>,
relay=mail.example.com[nnn.nnn.nn.n]:25, delay=149, delays=0/0/32/117,
dsn=2.0.0, status=deliverable (250 ok deliver to alternate)

kind regards/ldv