I think you should contact your ISP to help solving this issue, it seems it's not iredmail issue.

I solved some issues but I'm not able to send mail to a specific ISP with this error:

lost connection with
mail.register.it[195.110.124.132]
    while performing the HELO handshake

So I need to use a relayhost for all the domains are hosted by that ISP but I noticed that transport_maps is managed by MySQL...
What's the right way to configure that?
Should I use the domain table into vmail? What to put into transport field?

THX

I got same problems too...the clients send the mail and there is nothing in the log files...I don't get even bounces...sometimes the mail is received by the person on the other end sometimes not...I send messages to gmail.com, mail.ru, yahoo.com and sometimes the mail isn't received on the other side...but sometime it does...and when the mail is not received I don't get bounces, nothing

In my case I set postfix to relay mails to my ISP... some mails don't arrive yet, but I got some error messages at last...

I'm still facing some problems with my SMTP.

If I used local SMTP set up with iRedMail I have problems with some domains. Some domains don't receive my mails even if there are no errors in the logfile.

Other domains answer something like this:

relay=mail.register.it[195.110.124.132]:25, delay=5.4, delays=0.02/0.02/5.4/0, dsn=4.4.2, status=deferred (lost connection with mail.register.it[195.110.124.132] while performing the HELO handshake)

If I use relayhost option in main.cf my ISP's SMTP considers most of my outgoing mail as SPAM:

<john.doe@receiver.com>: host free.dsl.vodafone.it[91.80.36.30] said: 554
5.7.1 Message refused by DeepHeader check. This email has been rejected.
The email message was detected as spam.  (in reply to end of DATA command)

At now I'm not able to get my SMTP working. And I'm not able to understand why my ISP's SMTP reject only some mail from my server, yet.

Suggestions?