Inline / embedding attachments into email results in spam? Is this true?

When sending out one-to-one or transactional emails (i.e开发者_C百科. verification emails), can we include an inline / embedded attachment. Which is an image that displays our logo on the top of the email (HTML format of course).

I've read a few articles online, in particular this one:

http://ask.metafilter.com/84579/Creating-a-graphic-email-signature-without-attachment

Which says, that including embedded images could result in marking the email as spam. Is this why most verification emails I receive from third party services, don't include any images at all, just plain or even just HTML text?

---

it basically depends on how long your verification email is. there are spamfilters that check the text-to-image ratio since there are many spams that just consist of one short sentence and an attached or inline image which contains the spammy payload (they try to bypass the text content filter that way). also, there are systems that count the number of attachments with the same hash and mark your message as spam if you send to many of those to the same server. therefore its generally safer not no attach images (which won't be displayed on some email clients anyway).