When I send an email to an ISP non web based email account such as videotron.ca or sympatico.ca from my Gmail account in outlook 2016, the message is sent, Gmail records the message in the sent folder but then it is not sent to the recipient by Gmail. There is no error message that the message could not be delivered. When I try to send the email using another program such as Microsoft Mail or web based Gmail, the message is received by the recipient. There is no problem if I send a message from my Gmail account to another Gmail , Hotmail or other Web based email accounts. This behavior is occurring on both my computers. However when I set up the accounts at my sister's house, again using outlook 2016, there is no problem.
I have reinstalled office ( no change) , allowed less secure apps in Gmail, checked that all the IMAP settings for sending email is correct. I have set up another gmail account in Outlook, and again tried to send a message to a Videotron account. The same problem occurs. While it appears to be an Outlook problem, it may be that another program is affecting how emails are sent.
I am out of ideas. Can you help?