Virtru's support for aliases depends on the email platform being used.
Virtru offers full support for G Suite.
If you are employing a new alias, ask your G Suite Admin refresh your domain to ensure that your alias is recognized.
If you don't use G Suite and wish to open an email that was sent to an alias -- the secure message must be opened in the original inbox of the account that message was sent to. Trying to open a message that has been auto-forwarded to a different account will not work and is not supported by Virtru.