Emailing Link Subject Line

Hey y'all, thanks in advance. When I open any of my galleries, I select the very first photo and click on the 'share gallery' button. I then select 'Link' and then click on the email envelope. I select my recipients. I type in my custom subject line and then enter some text in the message block.
When everyone receives the email, the subject line is "Home <no-reply@smugmug.com>", not the original text I entered into the subject line.
Why?
How can I fix it?

Thanks again!