I can receive emails and still view all of my messages, drafts etc, and log in as usual. But I cannot send any emails!!

I have gone to the Add a phone page to verify my account with a mobile phone number. I was sent a text message with a four digit code in,
entered it when prompted, but I am still unable to send emails.  Please sort this problem out ASAP as this is a business account- I can not operate my business properly if I cannot send emails.
And there is no reason at all for this block to have been placed on this account.