[SOLVED] Intermittent Service Unavailable

[utkonos]

Some emails are being rejected as service unavailable. The connection from the PMG to the mail server is a LAN on private IP. I checked using netcat and there doesn't seem to be an issue. Is there a way to diagnose the root cause of this?

450 4.7.1 <test@example.com>: Recipient address rejected: Service is unavailable (try later);

 

[utkonos]

I understand. This is the greylisting feature. It is doing this to test if the sender is a normal mail entity or a spammer. A normal system will queue the email and retry after a period of time. The email is then accepted.

 

[Stoiko Ivanov]

I understand. This is the greylisting feature. It is doing this to test if the sender is a normal mail entity or a spammer. A normal system will queue the email and retry after a period of time. The email is then accepted.

Yes - exactly - the reply 'Service is unavailable (try later)' is used by greylisting

 

[utkonos]

Also, just for people who arrive at this thread, here are the configuration knobs that control greylisting:

Configuration > Mail Proxy > Options > Use Greylisting for IPv4
Configuration > Mail Proxy > Options > Netmask for Greylisting IPv4
Configuration > Mail Proxy > Options > Use Greylisting for IPv6
Configuration > Mail Proxy > Options > Netmask for Greylisting IPv6