Configuring e-mail sending for discourse

Bonjour,

Have e-mail sending setup for a discourse site which is working except e-mails are being flagged with this banner:

alert

Am not sure what causes this, if something in settings is not correct so e-mail can’t be validated as being valid (alert is from German e-mail company Tutao).

Can open help ticket with support team about this but checking here first in case anyone knows what is causing these flag alerts and how/if this can be corrected.

Thank you