In order to troubleshoot deliveries issues with your mail server, SpamHero makes it possibles to view raw mail delivery logs for clean messages. One particular error that can be confusing is the following:
Lost connection while receiving initial greeting
This error sounds like a connectivity issue, but it usually indicates a configuration issue with your mail server. The fact that our mail servers were able to get as far as the "initial greeting" means that our service was able to connect to your mail server, but that your mail server dumped the connection shortly thereafter. Here are some possible reasons why your mail server may have dropped the connection:
- Rate limiting. Because all of your messages come through our service first and then to your mail server, your mail server will think that all of your inbound messages are coming from very few IP addresses. If your mail server limits the number of messages that it will accept from a single IP address in a certain minute or hour, you may need to adjust or remove these rate limits to prevent this error from occurring.
- IP based access limits. While it's possible to only allow certain IPs to deliver email to your mail server using a firewall, many mail servers also allow you to allow or block email based on the sender's IP address. For example, see: Configuring Microsoft Exchange to only accept email from SpamHero.
- Firewall rules. It has been reported to us by a customer that they resolved this issue by adjusting the number of concurrent SMTP sessions allowed by a single IP. We are listing this possibility last because firewall rules usually block connections from even being made in the first place, which wouldn't make this error possible. However, we are listing this possibility here since at least one customer reported that adjusting this firewall setting fixed this error for them.
If you have discovered another issue that can cause this error, we welcome your feedback on how you resolved it.