Recently in 5.2.0 we have introduced complete Email Logging which is quite useful.
However, there seems to be a bug in Logging emails with very Long Email Body that are sent via Mailing List functionality. In particular this happens when we send emails with HTML in it (see attached).
Problem lead to the amount of data being stored in LogData column of EmailQueue table. Currently this field is a TEXT which is not enough to store Serialized logging data (html + plain versions) in it. I total ti takes (around 130kb). Then I have tried LONGTEXT, but it also failed why LONGBLOB worked out fine.
Strange enough we can see here that LONGTEXT should be a good match for this, but for some reason it didn't work
TINYTEXT 256 bytes
TEXT 65,535 bytes ~64kb
MEDIUMTEXT 16,777,215 bytes ~16MB
LONGTEXT 4,294,967,295 bytes ~4GB