How do you end your e-mails? Do you sign off with a “Best” or “Sincerely” the way you might with a letter or just type your message and click “Send”? And for that matter, do you include some sort of salutation at the start of e-mails or just dive right in?

This is more important than it might seem. When we communicate via e-mail, people cannot look us in the eye or hear our tone of voice, so they subconsciously search for clues about what we think of them. If we strike the wrong note with a salutation or sign-off, we could accidentally damage the relationship.

When e-mail first appeared most people didn’t bother to use salutations and sign-offs. It didn’t seem necessary—e-mails already included lines labeled “To” and “From.” But without any greeting or ending, e-mails came off as abrupt and off-putting.

Formality is the safest choice the first time you send an e-mail to someone you do not know well. Start with a “Dear Mr. Smith” and end with a “Best regards.” (“Sincerely” is a bit too formal.)

But when e-mailing an existing acquaintance, it’s fine to open with an informal salutation, such as “Hi”…and/or to use the recipient’s first name, if that’s the name you use when speaking in person. Here it’s fine to use an informal sign-off, too, such as “Thanks,” “Best” or “Regards.” (“Best” and “Regards” on their own seem less formal than “Best regards” together.) It’s also acceptable to use a short sign-off message such as “Thanks for your help” or “See you at the meeting tomorrow.”

Once you’ve exchanged e-mails with someone, the best option is to see what salutations and sign-offs he/she uses with you and then use something very similar in response—people tend to be most comfortable with people who seem most like them.

If an e-mail is work-related, avoid a salutation or sign-off that could be viewed as sloppy or unprofessional, such as “Happy Monday!” or “Go Packers!” or “Hey Joe.” And definitely do not misspell the recipient’s name in your salutation or refer to him by a nickname he doesn’t use—that’s an excellent way to make someone dislike you.

Drop salutations and sign-offs entirely only when several e-mails are exchanged in rapid succession. Such exchanges are more like conversations than correspondence—it would seem very odd to say “Hello” before and “Good-bye” after every utterance in a conversation.