Limit number of concurrent outgoing SMTP connections

[maxxer]

Hi.

We've recently deployed a Zimbra server on a Contabo VPS. We've done it in the past with no problems, but as a summer treat they started throttling outgoing SMTP connection, to prevent outgoing spam. Their support says they allow a maximum of 5 concurrent connections.

I found this to be problematic because when sending even single mails to several recipients I was getting connection refused messages:

Code: Select all

-Queue ID-  --Size-- ----Arrival Time---- -Sender/Recipient-------
CC7E3E2000C    50569 Fri Aug  3 10:37:10  xxx@domain.ch
(connect to YYY-com.mail.protection.outlook.com[213.199.154.138]:25: Connection refused)
                                         daniele.razzi@YYY.com
                                         eliska.a@YYY.com
                                         evy.m@YYY.com
                                         klara.a@YYY.com
                                         maite.e@YYY.com
                                         nadine.e@YYY.com
                                         puri.e@YYY.com
                                         raquel.a@YYY.com
                                         valeska.y@YYY.com

-- 49 Kbytes in 1 Request.

Is there a setting which could prevent these errors?
I thought Postfix would make a single connection to an MX for several mails.

thanks