can't send e-mail- smtp server offline or disappeared

Hi!

I've had issues sending e-mail from my @mac address for about a week. I can send from iCloud on the web but not from iPad, iPhone or MacBook.

Sometimes the server is offline, sometimes just not there at all - the error msg gives the smtp info and says I can't connect. Connection Doctor says everything is fine.

I've tried….

- turning off iCloud on all devices and re-booting

- removing a second e-mail account

- manually changing smtp settings

Receiving mail is fine.

can anyone help??!