Squirrelmail email address

[#1]

I recently sent an email using the compose/send within Squirrelmail (Webmail). The message was sent with an address myaccount@myaccount.plus.com, instead of the usual address mymailaddress@myaccount.plus.com.
This worked OK, the message was received by the recipient, who then used a reply to sender to send a reply to my message. But this reply does not appear in my inbox, presumably because myaccount is not set up as an address in Manage My Mail.
What have I done wrong? What can I do, if anything, to retrieve the message?

[#2]

If you've not got your catch-all switched on then you might not be able to retrieve the message.
To prevent this happening in future navigate to Options > Personal Information and change your email address.

[#3]

Thank you, Bob
Catch-all was set to 'Off', I have set it to 'On', if this gives me a problem with spam I'll just have to change it back. I also created a myaccount alias for my default address.
What I didn't realise was the email address set up by default in Squirrelmail was different to the one created as the default in Manage My Mail. I fell into an error trap which arises out of the way the account was created.
This explains why I haven't had the expected responses to emails I have sent recently from Squirrelmail. Are any of these likely to have been kept somewhere retrievable?