mail to (unknown user: "$")

[ifastsginfra]

Jul 4 18:28:53 nagiosXI postfix/cleanup[25358]: A48AA1E1252: info: header Subject: ** Host Alert: KWTEST78_copy_1_copy_1 is DOWN ** from local; from=<nagios@nagiosXI.localdomain> to=<$@nagiosXI.localdomain>
Jul 4 18:28:53 nagiosXI postfix/cleanup[25358]: A48AA1E1252: message-id=<20190704102853.A48AA1E1252@nagiosXI.localdomain>
Jul 4 18:28:53 nagiosXI postfix/qmgr[5319]: A48AA1E1252: from=<nagios@nagiosXI.localdomain>, size=702, nrcpt=1 (queue active)
Jul 4 18:28:53 nagiosXI postfix/local[25360]: A48AA1E1252: to=<$@nagiosXI.localdomain>, orig_to=<$>, relay=local, delay=0.02, delays=0.01/0/0/0.01, dsn=5.1.1, status=bounced (unknown user: "$")
Jul 4 18:28:53 nagiosXI postfix/cleanup[25358]: A6E761E1247: message-id=<20190704102853.A6E761E1247@nagiosXI.localdomain>
Jul 4 18:28:53 nagiosXI postfix/bounce[25363]: A48AA1E1252: sender non-delivery notification: A6E761E1247
Jul 4 18:28:53 nagiosXI postfix/qmgr[5319]: A6E761E1247: from=<>, size=2545, nrcpt=1 (queue active)
Jul 4 18:28:53 nagiosXI postfix/qmgr[5319]: A48AA1E1252: removed
Jul 4 18:28:53 nagiosXI postfix/local[25360]: A6E761E1247: to=<nagios@nagiosXI.localdomain>, relay=local, delay=0, delays=0/0/0/0, dsn=2.0.0, status=sent (delivered to mailbox)
Jul 4 18:28:53 nagiosXI postfix/qmgr[5319]: A6E761E1247: removed

I cannot find where is this unknown user $.
I have check under nagios CORE contacts and Admin -> mange users, all have email accounts.

anyone can help?

[scottwilkerson]

Can you show the configuration command you have specified for the host and service notification commands specified for this user?