kumomta/docs/tutorial/checking_logs.md

Check for success in the logs

Regardless of whether the mail delivers or not, you should take a look at the logs. Compressed logs are found in /var/log/kumomta/ as can be seen in this tree. Logs are segmented by a combination of size/time and stored in compressed files named after the time that the segment was started. To read these, you need to unpack them first. You have many options for configurating logging.

/var/log/kumomta
├── 20230311-033705
├── 20230311-033844
├── 20230312-182542
└── 20230314-181435

We can take a look at a specific log by decompressing it and since these are zstd compressed, you can view all but the current one with zstdcat. ZSTD is a streaming compression utility so the current file cannot be accessed until it is flushed and closed. You can force the current log to close by stopping KumoMTA.

Using the example above, we can see the content of the newest file after stopping KumoMTA with a zstdcat /var/log/kumomta/20230314-181435.

The default for log segments is to flush them after 1GB of data is written, but you can adjust them to flush after a certain amount of time. kumo.configure_local_logs has all of the available logging configuration options.