When you build the MIME::Entity, I don't think you can do

To => @ToAddress, CC => @cclist,

as I suspect the arrays will flatten into the parameter list. You should probably do something like:

To => join(',', @ToAddress), CC => join(',', @cclist),

or maybe you can pass an array reference (not familiar with what MIME::Entity can accept).

Also the advice to not escape @ in single-quoted strings sounds good to me.