Still waiting for implementation of Subject Line/Header in Textra.

Still need SUBJECT LINE just like Stock app... for many reasons, e.g. when u CC an email address so the recipient sees SOMETHING vs NOTHING on subject line.

Make it a Gr8 Day :)

@145636365-maggard (I wonder if that will work.)
I did notice that Textra does have (as every decent text app has) a setting to convert SMS to MMS when the chopping up messages exceeds a specified number.

You might have already guessed that mine is set to 1. I despise receiving multiple partial SMS's; they almost always arrive out of order.
So there's no way that I want to send such things!

With a proper SMS/MMS app, adding a subject does not necessarily convert a message to MMS.
Note: my experience is solely with Verizon.
Some apps will do as you have assumed, immediately convert to MMS.

On the contrary, if I send an email to myphonenumber@vtext.com and include a subject header, I will receive an SMS message with a subject.

That said, I'm shocked that Textra has no provision to add a subject at all.
It's as if their devs are ignorant of this part of SMS/MMS messaging.

is it possible this will be implemented?

yep. hoping this can be added

This also helps when typing a long message which you do not wish broken into multiple SMS messages. Adding a Subject converts the message to MMS and keeps the message together.