Can I make a suggestion.
When we add an extra field in the table 'vacation' like "email_name" and make adjusable in vacation.php / vacatin.tpl
First time that an "out of office" for an email address is created
mailname is created from $email and $name from table 'mailbox'
display it in the template.
With this in (vacation.php / vacatin.tpl) adaptable to the admin or user  customize it at your own discretion. eg
<DO NOT REPLY> firstname.lastname@example.org or leave it unchanged
It is therefore also useable if there would be a change in using a other module than vacation.pl
with "user control" you would be close to the user.
$ add_realname also comes in this config.inc.php
it's all just an idea but would love to hear your opinion
regards Jan Kruis