Before requesting support, we recommend that you review the following information.
The most common Connection Timeout errors are caused by:
- Connectivity issues.
- The system or software developed by the customer for sending and implementing retry/error interception.
- Outbound throttling on port 25 by the customer’s service provider.
- ContactLab-side throttling, when the configured limits for the customer are reached.
In the case of the first and second causes, you should check with your IT or development department. Often, the returned error is generated by customer software, and we do not know the logic that has implemented, or the problem that has been detected.
In the third instance, you need to understand the contract or service agreement limitations and similar, which are imposed by your provider, such as Amazon, Azure, Google and so on.
In the case of ContactLab throttling, the configured limits are generally not exceeded, because they are designed to ensure that you and our systems are protected.
It’s a good practice to use an SMTP forwarder (as a postfix), which natively handles instances and errors, as well as retrying the SMTP communications, as described in Using a local SMTP forwarder.
However, verification of the limits imposed by ContactLab remains valid, as described in the following:
- Maximum number of simultaneous SMTP sessions.
- Managing network issues.
- Inbound rate limiting at the SMTP listener.
As a further check that SmartRelay is working correctly on the ContactLab side, make sure that you have performed the Control and test procedure.