When answering a mail the name of the receipient is shortened

[J-and-F-and-S]

As soon as I answer an email from somebody who has a dot in his mail adress, Rainloop shortens the displayed name to the first name.

Example:
sandra.parker@mail.com becomes To: "Sandra" sandra.parker@mail.com

This looks like I have her mail address in my contacts with her first name. This is pretty inappropriate.

[RainLoop]

RainLoop does not do anything special with the mail address.
I checked your issue but cannot confirm it.

Сould you give me the example email with such problem ?

[J-and-F-and-S]

It's not about the mailadrress itseld, it's an issue with the the name that is automatically displayed for the contact. Please see my live example above. The guys last name is cut off and just his forename is shown.

It looks like I'm sending an email to an old friend, but it's a business contact here in this case.