If you do need to send an email to a group of people, as a courtesy to those you are sending to, please list all of the recipients e-mail addresses in the Bcc field. (Blind carbon copy - from the old days when typewriters used carbon paper to create identical copies of a document when it was being typed.) When an e-mail address is designated in the Blind carbon copy field, the recipient will get a copy of the email while their e-mail address remains invisible to the other recipients of the e-mail - some of whom they may or may not know. If you are not sure how to Bcc in your e-mail program, Microsoft offers great resource.
Long lists of e-mail addresses at the beginning of any e-mail is an immediate sign that the sender is either a novice or doesn't care to respect other's privacy. None of which are complimentary perceptions! E-mail addresses are like phone numbers. Only the owner of the e-mail address or phone number should be the only one to hsare it with others they want to use it.
By your sending mass e-mails to a list of people, you have made that decision for them - and that is bad, very bad. Let those you correspond with determine for themselves who they will make their e-mail address known to - do not make that decision for them! By listing handfuls of e-mail addresses in the e-mail headers for all to see is inconsiderate of each recipient's right to privacy.
What you might also notice is those addresses tend to follow the e-mail because people tend to just 'Forward' the e-mail instead of copying the information, pasting into a new e-am, and resending. This is where SPAMMERS tend to get long lists of e-mail addresses for future use.