Unable to receive emails on specific providers

You may be getting rejected if you have not setup SPF/DKIM/DMARC email verification and security configurations.

DNS Blackhole List (DNSBL) FAQs https://docs.aws.amazon.com/ses/latest/dg/faqs-dnsbls.html

Authenticating Email with SPF in Amazon SES https://docs.aws.amazon.com/ses/latest/dg/send-email-authentication-spf.html

Complying with DMARC using Amazon SES https://docs.aws.amazon.com/ses/latest/dg/send-email-authentication-dmarc.html

Authenticating Email with DKIM in Amazon SES https://docs.aws.amazon.com/ses/latest/dg/send-email-authentication-dkim.html

I'd suggest you start your analysis by looking at the any bounce feedback received for these undelivered messages.

To receive feedback notifications for messages submitted via the API, you need to configure SNS Topics to receive the published feedback. For messages submitted via SMTP, bounce NDRs are sent to the envelope sender (MAIL FROM:) of the submitted message.

See https://docs.aws.amazon.com/ses/latest/dg/monitor-sending-activity-using-notifications-email.html.

I am passing a similar issue, I will share here in case it can help.

I found that my emails sent from SES to outlook/hotmail were always sent to spam/junk folder, the main reason was that I am using configure set tracking open and clicks, where the email body has the awstrack.me link.

I did a test removing the configure set tracking open and clicks, then, when the email doesn't have the awstrack.me, the emails were sent to the other tab in hotmail, not send to spam/junk folder.

So, it is not a conclusion yet, but seems that emails that are sent with the track (awstrack.me), they are tagged as spam from outlook/hotmail.

In my case, I disabled the track open/click config set when the destination is outlook/hotmail.