We have several users that complain about not receiving only some of the emails our webservers send through AWS Simple Email Service. Most of those users not receiving emails are users with hotmail.fr email addresses.
We are currently using AWS SES without dedicated IP addresses (I'm in the process of collecting info whether using dedicated IP addresses could be a good solution).
The reputation of said emails is 9.9/10 according to mail-tester.com (DKIM, etc. are already enabled), and we're talking mainly about transactional emails here, so I don't think the problem comes from the quality of the email.
I have sent a support ticket to AWS and they replied the following
In regards to the list of messages to hotmail addresses in which you kindly provided, I have run a log dive on each of the emails and noted the following during my analysis:
Each of the messages was sent by '@.com' and returned a 250 SMTP status code. This means that the SES endpoint successfully delivered the email to the recipient mail servers. However, each of the emails that were sent to hotmail domains also returned with the message ' SMTP response message: Queued mail for delivery -> 250 2.1.5'. This includes emails sent to '*@hotmail.com, *@hotmail.fr, ***@hotmail.fr etc'.
As SES successfully sent each of the emails and because we have no further visibility into how the recipient server 'hotmail' deals with request and why is was queued, it is not possible for me to say why the Microsoft mail servers did not forward the email to the recipient.
As only Microsoft (hotmail) and Google (gmail) will have more information as to why the messages were queued, I would recommend reaching out to the respective teams to find out more information. Each Email Service Provider has their own rules and policies in place, and they have the last word regarding how the email is going to be accepted, rejected, queued or classified.
I am still in the process of figuring out how I can contact Microsoft/hotmail regarding this (I'm trying to find the appropriate contact form but is seems I cannot find the appropriate catrgory). In the meantime I'm also trying to find some stuff regarding this famous 250 SMTP code, but is feels like it's quite similar to a 202 Accepted HTTP code in a sense that the delivery actually worked, yet our users still don't receive the messages)
If you could help me shed some lights on this 250 SMTP code OR if you've veer had any experience with debugging users not receiving emails, I would gladly take the help.