I'm sending about 5000 transactional emails a month to various users. Things like password reset emails and other notifications - never any spam.
I'm currently using mailgun where I have a shared IP. What's happening is, about one a month my emails get blocked as spam as some other user on the IP is sending spam. I'm not talking about going to their spam folder - it gets blocked completely.
I then open a support ticket and they give me a new IP, but still a number of emails do not get delivered.
I don't mind paying for a dedicated IP, but they say at less than 50 000 emails a week a dedicated IP can have even lower deliverability.
What do you suggest I use for sending emails reliably?