Question on Soft Bounces
Context/background: Recently warmed dedicated IP. This process went very well. After warming we sent a promotional email and the deliverability is terrible (around 60%). Note: about 8 days between last warming email send and first promo email.
Problem: Majority of bounces are soft and have returned error messages for Yahoo, AOL and Verizon. The error message returned are all:
554 5.4.5 [internal] (last transfail: 421 4.7.0 [TSS04] Messages from 220.127.116.11 temporarily deferred due to user complaints - 18.104.22.168; see https://help.yahoo.com/kb/postmaster/SLN3434.html)
Other information: IP Sender Score/Reputation all looks great. IP is not listed on any blacklists (According to ReturnPath. MXtoolbox and Talos)
Question: How do you mitigate this type of soft bounce error? It seems to be the one issue we're facing.