MAILTOOL v10.41 SP161026b and higher now has a feature that was a customer request called "Test Mode".

In Test Mode no emails will actually be sent.

To start test mode, create a data area named MLTMODEDA (CHAR length of 10) with the value *TEST.

CRTDTAARA DTAARA(QTEMP/MLTMODEDA) TYPE(*CHAR) LEN(10) VALUE(*TEST)

This example shows the data area created in QTEMP.  The only thing you need to make sure is that the library the data area is created in is above any other possible data areas with the same name.