The sending server of my client email no longer works
monVPN replaces your IP address so your ISP’s SMTP server can no longer automatically identify you. monVPN blocks SMTP port 25 to block SPAM from our servers.
The solution is to use the SMTP with port 587 SSL or 465 SSL instead of port 25, as well as your email ID.
An authenticated SMTP has the advantage of working regardless of whether you are connected to the VPN.