Photos II - no invitation email

I've now created a second album and again I have issue with no invitation email being sent.

First time, the whole 'http://photos.readynas.com' link wasn't usable to access my nas, so I figured it was linked with that. Next day I was able to send the invitations.
Today, I've created a new album, but again no invitations were sent. This time the link 'photos.readynas.com' works fine, so it must be related just to the SMTP server used. Another option could be, that this time I tried to use the 'group' feature. But I sent an invite to my address as well, which didn't work either.

Is it possible to setup Photos II to use my email config from the frontview for sending the invitations? Just like the alert emails which are sent by my nas when there is an issue or a system update. I think this could help in case your server is unavailable.

I'm using Readynas PRO.

UPDATE:
Just realized that the emails are actually sent using the frontview email setup. What is strange though, is that the emails are not sent. I clicked on the 'Send Test Message' button in frontview and received an email almost immediately. Then suddenly after several seconds I've received also the invitations.
It seems like the emails just get stuck somewhere and hitting the test button has pushed the invitations through as well. Any idea how to fix this behavior?

Thanks