Connection to Outgoing Server Failed

[#1]

Since around Thursday last week I am repreatedly seeing this message on my Iphone when trying to send mails using IMAP. It receives emails but will not send. Any ideas ? I have not been migrated to Greenby yet but have recently received the email saying I soon will be. Anyone experiencing similar issues? 

[#2]

This is very similar to recent post : 

https://community.plus.net/t5/Email/Emails-won-t-send-with-SSL-enabled-from-iPad/td-p/2055046

[#3]

I have this too. I first noticed it yesterday, but I don't send e-mails from my phone very often.

Last time it happened I reported it in this thread but it resolved itself within 48 hours. The only difference is that this time I can neither send mails when connected to the internet via my home Wifi nor when connected through Vodafone. 

It only affects e-mails sent from my Android phone. Outlook on my PC works fine.

I haven't changed any settings and I have not been migrated to Greenby yet.

Any ideas?