mtalog filling up with old message records

[Matt .]

Hi Guys,

I have a strange issue from a MTA which had a DNS issue on the lookup
for it's a-record. Because of this a loop existed and all loop
messages got removed from the postfix spool.

What is happening at the moment is that the mtalog of Mailscanner is
filled up wit about 400K of records from time to time about this and I
cannot find where they come from. I can remove them but then after a
while they are added again:

30 Query     REPLACE INTO mtalog
(`timestamp`,`host`,`type`,`msg_id`,`relay`,`dsn`,`status`,`delay`)
VALUES (FROM_UNIXTIME('1515068227'),'backup-01','relay','3787FEEC01D','none','5.4.4','bounced
(Host or domain name not found. Name service error for
name=foo.bar.com type=A: Host not found)',SEC_TO_TIME('196'))

And this multiple times.

Why is this happening and can I fix it ?

Regards,

Matt