RegEx for PostMaster filter

[PiotrIr]

I’m trying to match body of e-mail with following pattern

condition

Body @micr
e-mail headers
X-OTRS-CustomerNo Microsoft

The trick is I would like to set this as case insentitive so could use @Micr, @miCr or whatever. Unfortunately can’t find RegEx which would actually work. From tester looks it should be:
/\@\bmicr\/i
But this doesn’t work. Could you advise please?

[crythias]

I believe the case is insensitive anyway. If not, [mM][iI][cC][rR][oO][sS][oO][fF][tT] is an option.