Hi, SES send SMTP sending well with Mautic. (On an other note, just for sending newsletters Mautic is not the best tool…)
Please check if you see 25k emails sent in your SES console.
If you see, that not all it is sent, check if you have any issue with rate limiting.
read this post:
It can happen, that your server is sending too fast, which can make your account throttled or the whole send just smokes away. That means Mautic thinks it’s sent, and Amazon just claims it never got them because the ‘door was already closed by them’.
Good luck