Apache error on send mail

[bpellegrino]

Recently i've started working with OTRS from scratch and creating a ticket support enviroment for several customers.
I'm about to put the system in beta for my collegue's, exept for a few error that haunt me since a couple of days.
After the usual switch from a crashing windows enviroment to a linux based enviroment things are running fairly good exept from this:

In a couple occasions apache seem to generate an error when it has to send an email:
[error] Couldn't send mail: 550 5.7.1 Client does not have permissions to send as this sender\n at /opt/otrs//Kernel/System/Email/SMTPTLS.pm line 167\n
First impression is that i've configured the email SMTPTLS wrong (we're using Office 365 for email purposes), exept that this error only occurs when users submit a ticket although i don't have set an event notification for new tickets.
When i'm sending a manually created event notification for a "ticket being handeled" or a "closed ticket" things go well.

As i'm writing this post i've found out that this has something to do with Agent Notifications (using default agent notifications for a new ticket configured from the Agent Preference panel). When i enable one of the them, the error will occur. Within the System Email Addresses Management OTRS creates a default email adres OTRS@localhost, which i've made invalid. I have allready created a support@ adress which is used for all email cummunications thus far for normal event notifications. Even when i make the OTRS@localhost invalid or change it to the same support@ email adres the same error will occur when i turn on Agent Notifications.
After this i'm looking if i have set a different email adress for internal purposes, but to no avail. All email is send trough support@, is there some way to find out which email is used to send agent notifications? i see that the within Frontend::Agent::Preferences, PreferencesGroups###NewTicketNotify the prefkey is UserSendNewTicketNotification, but thats how far i've come

[jojo]

the error is very clear:

[error] Couldn't send mail: 550 5.7.1 Client does not have permissions to send as this sender\n at /opt/otrs//Kernel/System/Email/SMTPTLS.pm line 167\n

You are not allowed to use the sender adress which is used (which might be empty (notifications) or another email adress from OTRS). So change your settings of your mail provider

[bpellegrino]

i figured out that much and i could change everything to the right setting if i could find out which email adres is used to send out Agent Notifications
Thing is, that mail does work (as stated). It's purely an error that happens when sending Agent Notifications. even while the only email adres used is ne that does work. Normal event notifications do work as intended.