Receive Connector Parameters for Ubuntu Postfix

Copper Contributor



first of all, please excuse me if my wording is off - I usually have nothing to do with Exchange and Servers in general and never have. 


We are sending mail from a linux server to a recieve connector via postfix. While sending a larger amount of emails at once (lets say 50 different mails to 50 different adresses at once), we regulary get an error and after a few emails the sending process stops.


I looked at the settings of our recieve conncetor and noted the following settings, that may be the source of this problem:


MaxInboundConnectionPerSource: 20

MaxInboundConnectionPercentagePerSource: 2


So the questions are:


1. Does Postfix establish multiple Connections at once? If so, would our recieve connector stop recieving mails if Postfix establishes more than 20 connections?


2. If at a single time, only this one system sends mails, thus the Connection Percentage of this one source is at 100%, would our connector stop recieving?


Thanks in advance and sorry for the unprofessional language.

2 Replies

Hello @jonisthl,

no need to apologize, your language is not unprofessional.

1. By default, Postfix typically sends emails sequentially, one at a time, without establishing multiple connections simultaneously. However, if you have configured Postfix to use multiple outbound SMTP connections or if you have multiple instances of Postfix running, it is possible for multiple connections to be established. In such cases, the "MaxInboundConnectionPerSource" setting on the receive connector can limit the number of simultaneous connections from a single source (your Linux server).

2. The "MaxInboundConnectionPercentagePerSource" setting on the receive connector determines the maximum percentage of connections that can be allocated to a single source IP address. If your Linux server is the only system sending emails and it reaches the configured percentage (in this case, 100%), the receive connector may start rejecting new connections from that source.

Based on your description, it is possible that the current limits set on the receive connector are causing the issue. To address this, you have 2 options:

- Adjust the limits on the receive connector to allow for a higher number of simultaneous connections from your Linux server, considering the number of emails you need to send.
- Modify the Postfix configuration to limit the number of concurrent email deliveries or adjust the sending rate to ensure it stays within the limits set by the receive connector.

It's important to note that the specific configurations and steps to adjust these settings may vary depending on your environment and setup. Therefore, it is recommended to consult with your email server administrator or IT support team for guidance that is specific to your organization's infrastructure and requirements.

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Kindest regards

Leon Pavesic

Hello @LeonPavesic
thank you for your detailed answer. I will have to discuss with our exchange colleague. After that I will message here again :)