Can't contact server results in rejected mail with no bounce

[creeble]

I've been testing PMG for several weeks across multiple domains, but just discovered a deal-breaker problem if it can't be solved.

I set up a domain with a valid MX record pointing to the PMG, but with a transport that points to a server that has port 25 shut off -- to simulate a temporary outage at the destination server. I have "Verify Receivers" set to Yes.

Here's what I get when I send it mail (from outlook.com):

2023-10-19T15:47:32.559490-07:00 pmg postfix/smtpd[642633]: connect from mail-co1nam11olkn2011.outbound.protection.outlook.com[40.92.18.11]
2023-10-19T15:47:32.998972-07:00 pmg postfix/cleanup[642635]: F3BBAC00B1: message-id=<20231019224732.F3BBAC00B1@pmg.real.dns>
2023-10-19T15:47:32.999899-07:00 pmg postfix/qmgr[642458]: F3BBAC00B1: from=<double-bounce@pmg.real.dns>, size=219, nrcpt=1 (queue active)
2023-10-19T15:47:39.008330-07:00 pmg postfix/smtpd[642633]: NOQUEUE: reject: RCPT from mail-co1nam11olkn2011.outbound.protection.outlook.com[40.92.18.11]: 450 4.1.1 <dave@domain-with-down-server.com>: Recipient address rejected: unverified address: Address verification in progress; from=<not-real-name@outlook.com> to=<dave@domain-with-down-server.com> proto=ESMTP helo=<NAM11-CO1-obe.outbound.protection.outlook.com>
2023-10-19T15:47:39.097904-07:00 pmg postfix/smtpd[642633]: disconnect from mail-co1nam11olkn2011.outbound.protection.outlook.com[40.92.18.11] ehlo=2 starttls=1 mail=1 rcpt=0/1 quit=1 commands=5/6
2023-10-19T15:47:46.665273-07:00 pmg postfix/postscreen[642584]: CONNECT from [147.78.103.182]:56887 to [66.42.80.17]:25
2023-10-19T15:47:46.774093-07:00 pmg postfix/postscreen[642584]: PREGREET 11 after 0.11 from [147.78.103.182]:56887: EHLO User\r\n
2023-10-19T15:47:46.990836-07:00 pmg postfix/postscreen[642584]: DISCONNECT [147.78.103.182]:56887
2023-10-19T15:48:03.056681-07:00 pmg postfix/smtp[642648]: connect to 216.32.74.103[216.32.74.103]:25: Connection timed out
2023-10-19T15:48:03.057448-07:00 pmg postfix/smtp[642648]: F3BBAC00B1: to=<dave@domain-with-down-server.com>, relay=none, delay=30, delays=0/0.03/30/0, dsn=4.4.1, status=undeliverable (connect to 216.32.74.103[216.32.74.103]:25: Connection timed out)
2023-10-19T15:48:03.057820-07:00 pmg postfix/qmgr[642458]: F3BBAC00B1: removed

It neither buffers the email for later checking, nor does it send a bounce to the sender; it just fails.

This is in contrast to our existing Barracuda server (which I would dearly love to replace) that buffers everything for up to 48hrs, rechecking every 15m or so. Once it can contact the server and verify the address, THEN it sends a bounce or whatever as necessary.

Is this behavior possible with PMG? If not, I guess I'm done experimenting, as we have several customers with mail servers that often have poor connectivity.

 

[Stoiko Ivanov]

It neither buffers the email for later checking, nor does it send a bounce to the sender; it just fails.

it rejects the recipient with a temporary error-code:

450 4.1.1 <dave@domain-with-down-server.com>: Recipient address rejected: unverified address: Address verification in progress;

(the 450 is temporary) - thus the sending server (outlook in that case) needs to retry at a later point (which it will do)

I hope this explains it

 

[creeble]

Yes, understand.

 

[josefb]

...
This is in contrast to our existing Barracuda server (which I would dearly love to replace) that buffers everything for up to 48hrs, rechecking every 15m or so. Once it can contact the server and verify the address, THEN it sends a bounce or whatever as necessary.

To my understanding the PMG will (because of postfix verify) also accept and buffer incoming mail when the final server isn't reachable but the recipient address has previously verified (and is in this verification cache).

 

[creeble]

@josefb thank you for that, having trouble verifying it because it's tricky to set up. But will try; it would be good to know.