Issue Mail are coming in really slow on Plesk server

[Next level web]

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Mail are coming in really slow on Plesk server

PRODUCT, VERSION, OPERATING SYSTEM, ARCHITECTURE

Plesk Obsidian v18.0.66_build1800241218.14 os_RedHat el8

PROBLEM DESCRIPTION

We receive with emails a delay of like 25 minutes. Sometimes faster but often with a delay especially when waiting on a verification code to login somewhere. We use Plesk mailing server. Clients domains struggle with this also,

STEPS TO REPRODUCE

Use Plesk email

ACTUAL RESULT

Delay of 25 minutes for receiving emails

EXPECTED RESULT

Receive email immidiatly

ANY ADDITIONAL INFORMATION

(DID NOT ANSWER QUESTION)

YOUR EXPECTATIONS FROM PLESK SERVICE TEAM

Help with sorting out

 

[Raul A.]

Hi,

Is the graylisting feature enabled?

Greylisting (Linux)

When the greylisting support components are installed on the server, greylisting protection is automatically switched...

docs.plesk.com

 

[Next level web]

Hi Raul,
I think it is enabled. What do I need to turn off?

 

[Raul A.]

Correct. It's enabled.

Deselect Switch on server-wide greylisting spam protection

 

[Next level web]

Ok I disabled it, hope it helps with the delay

 

[trialotto]

Ok I disabled it, hope it helps with the delay

Yes, it might help.

No, it is not certain to help.

In essence, greylisting functionality is one of the major culprits within the Plesk environment.

However, the DNSBL blacklist checks can also add to delays and/or the amount of mails (especially spam) can contribute to delays in mail delivery.

Naturally, there are many (many) other potential reasons for the delay.


I would start by investigating and to find out which domains are associated with major delays.

Those domains should be configured differently, in the sense that you add the reputable mails to the spam filter.

Those reputable mails will then - since they are whitelisted - automatically pass checks and be delivered almost instantly - the mail log should not contain a lot of "Milter-Reject" entries when you have whitelisted some domains.

Please note that this is not really feasible for all domains hosted by you, since it is rather time-consuming - however, it will help you figure out where and how the congestion in mail delivery occurs.

The whitelisting of specific domains is only part of the analysis - it helps you to dive into the actual cause of delays (if that cause differs from mails getting stuck into a queue or endless retries from external reputable mail servers that retry delivery after a milter-reject).

In most cases, you should be fine after whitelisting some domains ...... since it rarely occurs that the mail queue really gets congested.


It is important to note that the greylisting functionality can make a difference.

As a result, it is not always a good thing to disable the greylisting functionality.

So, when having done some investigation and having identified some offending domains, one should be able to re-enable the greylisting functionality.

In my experience, the whole mail server will work a bit better (and faster) with greylisting functionality enabled AND with whitelisting configured properly.


I hope the above helps a bit ....


Kind regards.....

PS Really bad domains should be blacklisted and even blocked with the Plesk Firewall. In essence, greylisting is a functionality on the "wrong level" - it is certainly better to block traffic before it reaches the server, hence implying that firewall usage is required and/or DNSBL blacklisting methods are required.