Emails don't bounce when sent through own server, and then hard bounce when sent through SES

[Gizmo321]

We are experiencing an unusual issue. Ever since we started using MailWizz our bounce rate has been higher than it used to be, and recently I discovered the following anomaly.

1. We sent a campaign using subscriber list X over our own VPS server. All hard and soft bounce handling limits are set to 1.

2. After the campaign finishes sending, several hundred email addresses have been removed from the list, so I know that bounce handling is working.

3. A few days later we email the same exact list using Amazon SES instead of our VPS. However the bounce rate ends up around 7%, most of which are hard.

Something must be going wrong; if all hard and soft bounces are removed from the list after sending through the VPS then the second campaign through SES should have a bounce of almost zero. What is going on here?

 

[frm.mwz]

Maybe your sending IP's (vps) reputation got a hit during the first non-SES sending, and if it (this IP) is visible somehow when you use SES, it now takes down also the deliverability of the second, SES send.

 

[Gizmo321]

Maybe your sending IP's (vps) reputation got a hit during the first non-SES sending, and if it (this IP) is visible somehow when you use SES, it now takes down also the deliverability of the second, SES send.

I thought SES would only show Amazon's IP, not our server's, is this not correct? Anyways we have replicated this issue several times with nearly the same bounce rates so while our server IP may not have a good rating, it is not getting any worse. Any other thoughts about what the problem could be?

 

[VVT]

@Gizmo321

if all hard and soft bounces are removed from the list after sending through the VPS then the second campaign through SES should have a bounce of almost zero. What is going on here?

This is possible, we don't know what rules have been set at the receiving ISPs. After analyzing your first email, they might possibly have decided not to accept future emails of same nature (comparing from domain, profile of email, links or whatever).

But, I'm not guessing here, take a look at the bounce report for that campaign (campaigns > campaigns > "i" for the said campaign > View details for "Bounce rate"). Bounce messages will reveal the exact reason and you can start investigating from there.

 

[Gizmo321]

@Gizmo321



This is possible, we don't know what rules have been set at the receiving ISPs. After analyzing your first email, they might possibly have decided not to accept future emails of same nature (comparing from domain, profile of email, links or whatever).

But, I'm not guessing here, take a look at the bounce report for that campaign (campaigns > campaigns > "i" for the said campaign > View details for "Bounce rate"). Bounce messages will reveal the exact reason and you can start investigating from there.

I clicked the details button for bounce rate but it does not show the exact reason, it only says hard or soft. How can I find the exact reason?

Also I noticed that almost all of the bounces for the campaigns sent on our VPS are from Yahoo and Hotmail accounts, while the bounces for the SES campaigns contain zero yahoo and hotmail addresses, and only .edu and company emails.

 

[frm.mwz]

Yahoo, Hotmail and similar ones have specific delivery procedures, especially rates, eg no more than xx per hour, that if you send from your own VPS, must try to obey, as otherwise you get slowed down, greylist checked or blacklisted. That's why it is best to use a very well adjusted 3rd party delivery sender. Sending email otherwise becomes a full time job

(Have not checked in detail recently, but last time I checked it was about no more than 50 emails / hr and 200/day from one email address and/or IP. So if you have 10k hotmail, then you need to spread it out nicely over IPs, from addresses, time, etc )

Also, different recipient servers react in various ways to different senders (incl their original IPs, delivery servers, even used sending software if detectable in the header, etc, so best to keep it diverse/natural/nonrobo).