Exim is unable to deliver emails.
A busy mail server may have an increased number of connections, and when configuration limits are reached any further connections are denied. The Exim log file /var/log/exim_mainlog will show output like the following.
2023-01-26 17:14:12 Connection from [192.168.20.1]:45774 refused: too many connections
The Exim smtp_accept_max setting can be increased to accommodate the server's requirement.
- Go to "Home / Service Configuration / Exim Configuration Manager"
- Click the Advanced Editor tab
- Search for smtp_accept_max
- Change the value as needed. Example: 200
- Scroll down and click save