How can you solve "increasing size of log file" problem in Mailbox Database in Exchange 2016?

Are you running the appropriate backup maintenance so that the log files get truncated? Once the database is properly backed up, the log files should truncate also enable circular logging but be aware that with circular logging enabled you can recover data only until the last full backup

Backup or enabling circular logging on databases

ensure the Database is correctly being backed up by your backup solution or enable circular logging on the database.

As suggested above, either ensure the Database is correctly being backed up by your backup solution or enable circular logging on the database. Enabling circular logging will delete the log files, subsequently taking away your ability to recover logs from anywhere because you are deleting it. This approach is not recommended. The best is to ensure the database backups are regular so backup software takes care of the log truncation.

We can do full or differential backup for DB to purge the log file or enable circular logging to stop generating them.

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