Can SIGNL4 query a mailbox?

Not yet out-of-the-box. SIGNL4 cannot directly query an email mailbox (e.g. via POP3 or IMAP).

Instead, emails need to be routed to the email address each team gets in SIGNL4. You can for instance create a mailbox rule in your mail program to route all or specific emails to the SIGNL4 team email.