Looking for a commercial outgoing SMTP server for my domain

Hi,

I hope this is the right place to ask, even if this group seems rather
quiet recently (I never posted here before, but I browsed it before
posting).

I've been running an email service for my domain for the last 25 years,
and I have to admit -- I have enough. I have everything configured, SPF,
DKIM, TLS (with free Let's Encrypt certificates), my email server
reputation, according to some online tools, is great, I never sent any
spam, but my outgoing emails seem to be blacklisted (not rejected /
bounced, just dropped) on some large servers based on who knows what.

It got to a point where I send an email and have to call the person if
they received it (and they often don't).

I run the server (Postfix) on a cheap VPS, which might be the issue. But
the IP is mine only, and has been mine for several years before.

I have enough. I'm looking for a commercial SMTP relay. I want to keep
incoming email on my server, but relay outgoing mail somewhere else.

It has to support wildcards, as I don't use a single email address (I
create an alias per-usage, to track and fight spam).

Basically some SMTP server that will let me authorize and send emails as
any user from my personal domain.

I've been looking through such services, but they all seem to be aimed at
supporting mailing lists, mailing campaigns, transactional emails, etc. I
don't run anything like that. Just a low-volume, personal email service
used only by me.

Is there anything you could recommend that's reasonably cheap and will
make me forget about problems with deliverability?

Thanks in advance.

--
A synonym is a word you use when you can't spell the other one.