Depending on the level of the request/email, I often start meeting requests with simply "Attention" or "Dear Recipients".  I also use the "Hello All" for less formal and by name if it is one individual (first names if I know them, Ms/Mrs/Mr if I don't).  For very formal, or if I have never met someone I'm sending a request to it's "Sir" or "Ma'am".  (ie "Ma'am, so-and-so has asked me to schedule a meeting between yourself and...")  It's a nice opener, polite, and professional without it being a formal letter.



Just a reminder to us all... e-mails are something that get forwarded all over without our knowledge so anything we draft and sends should be in such a format that we will not be embarrassed to have others read.  I recently sent an e-mail to a co-worker which ultimately went to the Company President.  Thankfully I was polite and professional even though the original sender and I are buddies, but it reminded me to mind my manners in ANY e-mail communication since it is a permanent example of my communication skills.