After fix the problem about Method 6 in Windows Server, I was testing another scenario using Method 5 that should launch Outlook but that didn't happen.
So I decided to use the simple test printing a small file with these basic commands:

//PDFX,Save.ShowSaveDialog,0
//PDFX,Save.App.Run,0
//PDFX,Save.WhenExists,1
//PDFX,Email.Method,5
//PDFX,Email.To,"tavares@umzero.pt"
//PDFX,Email.Content,"Junto enviamos o Recibo 00172 Cumprimentos."
//PDFX,Email.Subject,"Envio de Recibo"
teste

With Method 5 I get <PRINT:4cc9> MAPISendMail error: 2 but it works perfectly using Method 0

As far as I know, both should do the same but preferebly use method 5, no?

I've adjusted ny program to use method 0 but would like to confirm and report in case there is something needing a fix.

Thanks

For what it's worth, Methods 5 and 0 seem to work more or less equivalently on my Windows 10 laptop. The main difference is that Method 5 is implemented via calls from A-Shell to the MAPI library, whereas Method 0 is implemented via similar (but opaque) calls from the PDFX driver to the same library. But obviously if the internal PDFX version works better, you should go with it. (And probably we should do some further investigation and maybe update some libraries.)