The default for SiteSetting.delete_email_logs_after_days has been reduced to 90 days as per
https://github.com/discourse/discourse/commit/186623acd070b71422dfe61e083fa3aeb67844ac
For busy sites that send out alot of emails, this table can bloat fairly quickly. There are some optimizations that we can do on the table to make it use less disk space but that’ll have to wait till Discourse Version 2.1.