Send Email itself is a service (see http://www.tersus.com/#Id=43), so there's no requirement for it to be encapsulated in a service, but up until the version 2.1.16 support for error exit's outside a service (and on the server->client threshold) was practically non-existent, and so wouldn't work in your case.
The practical solutions to this is either encapsulating Send Email in a service leaving the error exit on Send Email which is no longer on the threshold and should fire, or updating to a later version (see http://www.tersus.com/#Id=239).
I would like to point out that the fact that Enviar is a client process means that each time it is executed, it performs 3 separate server calls, one for each of sv_mensagem, Servidor_email and Send Email. This seems totally unnecessary and certainly hurts performance, so it seems to make sense to convert Enviar itself to a service (you can use right-click>Change Plugin for that), which will also resolve the original error exit issue.
Doing so will cut the number of server calls related to Enviar by two thirds, but still leaves multiple server calls, since Enviar itself is repetitive, so in actual fact it seems you should encapsulate Enviar (and possibly other servier calls before or after Enviar) in a Service, so that sending any number of emails results in a single server call.
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