We moved a website to EB a few weeks ago. Ever since the move not all the emails are leaving the site. We have scripts that send single email and scripts that loop through and send out multiple emails.
We're sending the emails via SMTP, these are rooted through a third party provider. Today we changed the third party to be SES with the hopes that would solve the issue.
I've done a few tests but it's still happening....
We still have the site on the old platform and it works perfectly there..... I'm wonder if we're missing something?
Could it be, that your eMails (or better: your IP) are classified as spam?
The problem with eMail today is, that because of spam, also legitimate eMail senders can easily come on spam lists and thus be blacklisted. They will have a lot eMail bounces or eMails that never reach their destination.
That is what, special eMail providers have their business build on.
Your old system might be still white-listed, but your new system is not, since services that come from one day to another with a high load, will be easily blacklisted.
Those blacklists are IP based and I also heard, that specially cloud hosting services are hit by this, because many spam senders use cheap cloud services.