Outgoing email from my static IP line (denied by google etc)

I am setting up Mailcow to eventually move email off Google Apps completely

However, it seems that Google (and likely many other?) providers will not accept email from my IP address:

host aspmx.l.google.com[74.125.68.27] said: 550-5.7.1
    [xxx.xxx.xxx.xxx] The IP you're using to send mail is not authorized
    550-5.7.1 to send email directly to our servers. Please use the SMTP relay
    at 550-5.7.1 your service provider instead. For more information, go to 550
    5.7.1  https://support.google.com/mail/?p=NotAuthorizedError
    ..... - gsmtp (in reply to end of DATA
    command)

The linked page says:

What can I do to fix this?
Your ISP may provide SMTP relays which will accept mail from your IP, and these servers should be authorized to send mail. Some ISPs may provide a way to get an IP that is authorized, either by upgrading to business class service or static IP service. You should reach out to your ISP to see what options are available.

Another alternative is to send mail through your own domain’s servers, either by configuring them to allow relay from your IP address, or by using MSA (mail submission agent). Learn how to use Gmail to send mail from a different address.

Please note that we are unable to allowlist IP addresses or otherwise make exceptions.

My service provider does not offer email for outgoing at all.

setting up an SPF record for my domain(s) listing my (static!) IP does not help

What do others do in such a situation?