Is SMTP plugin necessary?

Hello,

After 3 years of having my contact form working perfectly (with contact form 7 plugin) it stopped working 3 weeks ago. I contacted hostmonster support (my hosting) and they fixed it. Later I realized they installed wp-mail-smtp plugin in my wordpress.
I would like to know your opinion about this as I prefer to have as little plugins as possible.
Is this plugin real necessary for the contact form to work or it is fixing some Hosting anomaly?

Thank you,
Luciano