The mail server is working perfectly, suddenly clients call saying that the email are not being delivered or received.

We check the Spool and find it growing to hundreds and thousands if we leave it without any action.

The only solution is to Stop and Run the smartermail service and the spool works for 24 hours without any issue, then at no reason, the same issue happens.

i got this error log 

[2021.04.12] 23:29:28.922 [47923418] Added to SpamCheckQueue (49 queued; 50/50 processing)
[2021.04.12] 23:29:28.922 [47923428] Added to SpamCheckQueue (50 queued; 50/50 processing)
[2021.04.12] 23:29:28.922 [47923438] Added to SpamCheckQueue (51 queued; 50/50 processing)
[2021.04.12] 23:29:28.922 [47923388] Blocked Sender Checks completed.
[2021.04.12] 23:29:28.922 [47923444] Blocked Sender Checks completed.
[2021.04.12] 23:29:28.922 [47923416] Blocked Sender Checks completed.
[2021.04.12] 23:29:29.891 [47923397] ClamD Checks error: No connection could be made because the target machine actively refused it 127.0.0.1:3310 | error
[2021.04.12] 23:29:29.891 [47923449] ClamD Checks error: No connection could be made because the target machine actively refused it 127.0.0.1:3310 | error
[2021.04.12] 23:29:29.907 [47923397] Unable to parse Command Line Path: C:\SWSoft\Plesk\admin\bin\smmailfilter.exe %filepath
[2021.04.12] 23:29:29.907 [47923397] Command line exe finished.
[2021.04.12] 23:29:29.907 Calls to ClamAV have failed many times.  Restarting the clamd process...
[2021.04.12] 23:29:29.907 [47923480] ClamD Checks error: No connection could be made because the target machine actively refused it 127.0.0.1:3310 | error
[2021.04.12] 23:29:29.907 [47923480] Unable to parse Command Line Path: C:\SWSoft\Plesk\admin\bin\smmailfilter.exe %filepath
[2021.04.12] 23:29:29.907 [47923480] Command line exe finished.