One quick tip is to also ensure your source data is clean of duplicate emails.You don't want to do a 50/50 random sample, and then have two records with the same email address (Rec...
I've been monitoring our email bounces, and for one of our most recent email sends, we had a large number of bounces with the bounce reason:
554 5.4.7 [internal] (last transfail: 4...