Mal did speak thusly:

Dear Patrick, Thank you very much for your reply.

...

What MTA are you using?

Postfix latest version.

Checking the logs that you suggested, I found the cause for this delay, however, do not know how to get around it...

When I am sending mails to the list from any other smtp server than my isp's (from webmail etc), the delivery is instant! However, when I send a mail from my isp's smtp server (which is the same smtp that postfix is using to send all mails that are posted to my list), then delivery takes about 1 hour!!

Does anyone know why that could be? Is it confusing my isp's smtp server???

Thank you for your help. Mal

---------------- End original message. ---------------------

Sounds like they have implemented greylisting as an anti-spam measure and have set the retry period to an hour.

Do you see anything in your MTA logs that looks something like this?

reject=451 4.7.1 Greylisting in action, please come back in 00:10:00

If so, you need to get with their sysadmin and have them whitelist your mailman server.

Dragon

  Venimus, Saltavimus, Bibimus (et naribus canium capti sumus)