"[Blank]" in email subject line.....what does it mean?

[#1]

May I be very cheeky and ask a question relating to some emails received on a friend's btinternet a/c?
Regards....

[#2]

It probably means that the message sender simply forgot to enter any text in the "Subject" box,
then either the email sending program automatically inserted "[Blank]" rather than sending nothing as a subject,
or the receiving email program displays "[Blank]" to indicate that there was nothing to display.

[#3]

It simply means that your friends were to lazy or couldn't be bothered to enter a subject for the email and your email client as added the [Blank] to tell you this.
I find this annoying myself as it makes searching for them later tedious. But that's me  

[#4]

Thank you so much for your replies, however, stupid me, the added word is not "Blank" it is "Bulk."
I came across it a long time ago and I can't place the significance.
Any new thoughts?
Regards...

[#5]

Some emails received on a friend's btinternet a/c has the word "Bulk" added to the Subject line.
Any ideas what this means?
Regards....

[#6]

Topics merged.

[#7]

Again this has either been added at the sending or receiving end and means that you are not the only recipient of the email. When sent a BCC (Instead of a To) was used to send the email to multiple addresses at once and may indicate spam. As far as I recall this is what Outlook does (did).
Edit - Corrected typo.

[#8]

Thank you Mook.
Up to 10-years ago, I used BTInternet and, as a result of the comments, I now seem to remember that "Bulk" was added to the subject line by BT to indicate a mass distribution, that suggested a possible unwanted message carrier.  I suspect you could then decide whether "Bulk" mails should be eliminated at server-level, at user-level or allocated to a folder apart from the rest.
Thank you everyone for your responses, you have jogged my memory!
Regards and thanks....Noel