421 4.5.1 No more messages on this connection http://tele.dk/25153

tele.dk is an ISP from Denmark. As per the Postmaster guidelines, tele.dk mail servers do not accept more than 3 messages per connection, if you attempt to send more emails, you would get the following error message :

421 4.5.1 No more messages on this connection, see http://tele.dk/25153

The following quick How-to explains, how to configure Postfix to limit number of messages per smtp connection / session to danish domains which are hosted by tele.dk.

Note: The following configurations worked on Postfix 3.2.3.

Add the following to /etc/postfix/main.cf

# mail.dk transport
transport_maps = hash:/etc/postfix/transport
teledk_initial_destination_concurrency = 3
teledk_destination_concurrency_limit = 3

Add the following to /etc/postfix/transport

.mail.dk        teledk:
.tdcadsl.dk     teledk:
.tele.d         teledk: 
.dknet.dk       teledk: 
youseeme.dk     teledk:
besked.com      teledk: 
beskedboks.dk   teledk: 

You can add more domains by reviewing logs. These are some of common domains. “.mail.dk” refers to any subdomain.
Add the following to /etc/postfix/master.cf

teledk unix    -       -       n       -       -       smtp

Update lookup table

postmap hash:/etc/postfix/transport

Reload Postfix

  systemctl reload postfix