Restricted ports

Hi,

We are sending email through our SMTP account, SMTP-STARTTLS, Plain, Port 587 using Post SMTP on a site at WP Engine.
However according to WP Engine this should not be possible:
“WP Engine utilizes Google Cloud servers, which restrict the standard outgoing email ports (25, 465, and 587)”
It´s really awesome that we are able to use 587 with Post SMTP since we don´t have access to any alternative ports (from what I know Post SMTP is the only plugin that succeed with this).
But I was hoping you could comment on how this works and if it´s safe to keep using this setup?

Thanks!