Postfix keeps sending same email over and over

Hi, community.

I’ve got a problem, when Postfix keeps sending me same email from one of my websites over and over, periodically every 5 minutes. I just can’t track what keeps sending it and wh.

log:
Jun 25 19:02:10 srv postfix/qmgr[17283]: 8D5269C1559: from=<yyy>, size=599, nrcpt=1 (queue active)
Jun 25 19:02:11 srv postfix/smtp[17297]: 8D5269C1559: to=<xxx>, relay=gmail-smtp-in.l.google.com[2a00:1450:400c:c08::1b]:25, delay=0.51, delays=0.05/0/0.16/0.3, dsn=2.0.0, status=sent (250 2.0.0 OK 1593100931 g139si3971190wme.177 - gsmtp)
Jun 25 19:02:11 srv postfix/qmgr[17283]: 8D5269C1559: removed

No specific configurations were made to postfix. Only plain Virtualmin server with wordpress and contact form.Mail is fully signed with DKIM, SPF, DMARC. xxx is my email I use for testing, it’s not integrated into the website form.This can be used as an admin mail for the virt server, but I’m not sure where to check it.
This situation looks like the mail is trapped in a loop.

Tried cleaning queue with these - nothing:
sudo postsuper -d ALL
sudo postsuper -d ALL deferred
sudo postfix flush

Where should I look to resolve this problem?

Appreciate your help,
Oleh

There’s an update. I stopped postfix service, but mail queue is keep filling. I suppose problem can be related to the site itself, bu I’m not sure.

Phpmailer on the website would be my first point of contact. Check it out. Disable the website mail function and then see if your que stops increasing.
Also, if the website is wordpress, ensure you have a security plugin like wordfence installed…enable recaptcha on the contact forms etc.

Thanks for the advice - you were totally right.
Queue still was filling with this same message, so this is a definitely a website issue.
Strangely enough, this wasn’t the case on another server.

Will continue investigation on a website, thank you.