Hi, I cannot send email with Mac Mail

Arthur R. Demers wrote:

I can receive email in Mac Mail but cannot send, I called my ISP and they verified that my settings are correct. I can send email with my ISP's webmail page. Thank you for any help with this.

Use the Connection Doctor for some clue...

Mail>Window>Connection Doctor> Show Details

Use Connection Doctor in Mail on Mac - Apple Support

If no insight or resolve—

For problem accounts the go to way to sort things out is to delete the account, then add it back.

Remove email accounts in Mail on Mac

Remove email accounts in Mail on Mac - Apple Support

Add email accounts in Mail on Mac - Apple Support

Add email accounts in Mail on Mac - Apple Support

Note—

IMAP accounts stay on the server, so no local loss, when you re-sync

POP accounts download and remove from the server—therefor save your inbox/sent box if you want them

On My Mac" is just that, local folders you created and moved mail into. So no loss

more: https://support.apple.com/mail