Please allways check infos like this:
if you have access to a terminall compare the result from:
sudo -u www-data php occ config:list --private |grep "\"mail_s"
with the infos from your email provider. Be accurate and have fun 
Please allways check infos like this:
if you have access to a terminall compare the result from:
sudo -u www-data php occ config:list --private |grep "\"mail_s"
with the infos from your email provider. Be accurate and have fun