If enabled, the "Custom welcome message" sends an email from the first teacher in the list. However, this teacher is not necessarily the teacher in charge of the course and students will end up replying to the wrong person. It would be better if the email could either be sent from a specified teacher, or if it came from the generic noreply Moodle address.

Here is one other example of where the custom welcome message has had to be turned off, since the sender cannot be defined: https://moodle.org/mod/forum/discuss.php?d=136806