OP here. To add a little context.

I have been using SendGrid for the past year and their deliverability rate has gotten down 13%. I am getting 5-10 emails every day from users claiming that they don't receive the email. I have 99% reputation BTW. So the problem does seem to be SendGrid since I barely send > 40K emails per month.

So I have been thinking of either self hosting via Postal or using Amazon SES. However, I haven't used any of those before so don't know the downsides. I am particularly concerned about deliverability.

Hope someone can shed some light on this.