Thunderbird

Tools > Account Settings

Outgoing Server (SMTP) > [Add…]

Settings

Description: RealSender
Server Name: rsxxx.realsender.com
Port: 587

Security and Authentication

Connection security: STARTTLS
Authentication method: Normal password
User Name: (the one we sent you)

[OK]

RealSender > [Set Default]

Account settings
(select you email account on the tree at the left side)

Outgoing Server (SMTP): RealSender

[OK]

The first time you send a message

Outgoing Server (SMTP) Password Required

Enter your password for…: (the one we sent you)

[x] Use Password Manager to remember this password

[OK]