The default configuration of Odoo.sh instances should work.
The catchall address must use a domain which is associated to Odoo.sh database.
If your database can be accessed using yourcompany.odoo.com,
the catchall domain can be @yourcompany.odoo.com.
This is the default configuration done for new Odoo.sh databases.
If you setup a custom domain in your Odoo.sh project settings, you can use that domain as well.
you configure mail.yourcompany.com in your custom domain in your Odoo.sh project settings,
then you can use @mail.yourcompany.com.
Of course, in your domain registrars, you need to create a MX record mail.yourcompany.com pointing on yourcompany.odoo.com.
That said, after viewing your database logs, I do not believe the issue comes from a mis-configuration of your email alias. Indeed, evidences the replies arrived can be found in your logs, but Odoo couldn't find the original message to which this reply is addressed:
/home/odoo/logs/odoo.log.1:2018-07-13 15:47:38,036 4 ERROR xxxxxxxxxxx-xxxxxx-odoo-com-xxxxxx-xxxxx odoo.addons.mail.models.mail_thread: No possible route found for incoming message from "Bruce Letterle- xxx xxx Xxxxx" <email@example.com> to "Xxxxxx Xxxxxxxxxx" <firstname.lastname@example.org> (Message-Id <email@example.com>:). Create an appropriate mail.alias or force the destination model.
/home/odoo/logs/odoo.log.1:Traceback (most recent call last):
/home/odoo/logs/odoo.log.1: File "<string>", line 6, in <module>
/home/odoo/logs/odoo.log.1: File "/home/odoo/src/odoo/addons/mail/models/mail_thread.py", line 1300, in message_process
/home/odoo/logs/odoo.log.1: routes = self.message_route(msg_txt, msg, model, thread_id, custom_values)
/home/odoo/logs/odoo.log.1: File "/home/odoo/src/odoo/addons/mass_mailing/models/mail_thread.py", line 31, in message_route
/home/odoo/logs/odoo.log.1: return super(MailThread, self).message_route(message, message_dict, model, thread_id, custom_values)
/home/odoo/logs/odoo.log.1: File "/home/odoo/src/odoo/addons/mail/models/mail_thread.py", line 1184, in message_route
/home/odoo/logs/odoo.log.1: (email_from, email_to, message_id)
/home/odoo/logs/odoo.log.1:ValueError: No possible route found for incoming message from "Bruce Letterle- xxx xxx xxxxx" <firstname.lastname@example.org> to "Xxxxxx Xxxxxxxxxx" <email@example.com> (Message-Id <firstname.lastname@example.org>:). Create an appropriate mail.alias or force the destination model.
What's important when a customer reply is sent to your database is:
- the fact it uses your catchall address as the recipient (email@example.com),
- the message as in its `references`header the `message-id` to which it replies, so Odoo can find back the original message to which this email is addressed.
The fact Odoo couldn't find a possible route for your message can have multiple causes:
- The document from which the original mail was sent has been deleted,
- The customer used the button "New mail" and copy/pasted the recipient instead of using the "Reply" button, in such a case the `message-id`is not set in the `references` header of the email,
- The email client does not respect the email protocol and omit to set the `references` header correctly,
- The email server from which was sent the reply drops the `references` header.
From experience, the most-likely cause is one of the two firsts stated above.