'Incorrect greeting' usually means the authentication method is wrong, or some other setting. It also happens when you try to send over a non-secure port through a network not belonging to the mail provider. What are your smtp settings, and what is the antivirus?

My antivirus is McAfee - I try turning off the firewall and sending a message and that did not work (so I turned it off).

My ISP is Bell - is that what you mean by SMTP settings? I checked with their settings and the Server Name and Port are correct (I tried changing the port to 25 which did not work so I changed it back to 587).

Tools/Account Settings, Outgoing Server (SMTP) at the bottom of the left pane. The recommended settings are:

smtphm.sympatico.ca on port 587, STARTTLS security, authentication = normal password, User Name = email address.

The McAfee firewall is probably not a factor, but you should disable mail scanning.

Please keep the ideas coming!

The SMTP setting are accurate.

I could not find a an option to not scan outgoing emails so I turned off real time scanning altogether. Alas, the problem persists.

I think you will have to test Windows in safe mode, as this is the only reliable way to eliminate McAfee, a perennial problem with TB, as the source of the issue. It shouldn't be necessary to entirely disable real-time background scanning, just its action on email.

sadly, i could not figure out how to get connected to the internet in safe mode with network - i ensured that the network adapter was enabled in the device manager and re-started the WLan AutoConfig. soooo, i am not sure how to test tb in safe mode without access to mr. internet there

Uninstall McAfee, restart the PC, and then try TB. If you have an Ethernet cable, connect the PC directly to the modem/router and temporarily disable the wifi adapter, so safe mode with networking is easier to apply.

I downloaded a McAfee update - problem continued. So, I purged McAfee from my system - problem persisted. I can't get access to an ethernet cable.

So... (sadly) go back to Outlook? I really don't want to.

Hard to say what the problem is, so I'm reduced to asking about obscure factors. Did sending ever work, and when it stopped, what changes could have been made at that time? Are you using a VPN? Did you restart the modem/router? Can you send with a different service, such as gmail? Did you change a password or apply two-step verification on the account (if it's available from Bell)? Did it stop working after a TB update? Check the Update History in Options.