When P100 first mentioned it, I did some research on it to find out that senditfake (and the other equivalents) were not able to disguise the email header information. You'll find lots lots of history on that particular topic and them on-line.
In the process I also discovered that this particular service was no longer active. It apparently has been recently sold and some are speculating that a spammer may be using it to collect e-mail addresses? But either way, this particular service is not currently active.
Anyway, I didn't want to dilute the other thread with that side information as it wasn't as relevent. I just took P100's comments about them as if she had said "or other equivalent services".