I found that https://www.ads-software.com/extend/plugins/swift-smtp/ worked on my 2.6.x installation. I had to enable the php openssl and also did sockets at the same time but the settings are fairly straightforward.
I also changed it so that the Settings->General->Email-Address was the same as the user that was configured in the switft-smtp plugin.
Other smtp plugins
cimy
https://www.cimatti.it/blog/cimy-wordpress-plugins/cimy-swift-smtp/
or
Coffee2Code SMTP plugin
https://coffee2code.com/wp-plugins/configure-smtp/
