Please include the addressee in error log messages for mail failure. Are failed messages stored anywhere? If so, for how long?
The other thing I expected was to be able to find in the database a record of subscribe attempts where the email send failed. The most promising table was members_subscribe_events, but it only contains successful events. email_recipients looked promising, but no dice. That is still an empty set for me.
Ghost is all about engagement. Attempts to subscribe are pure gold. Yet if email is not working (and how often is that the experience?) that person’s email is just flushed down the toilet, it seems.
I am weeping bitter tears.