First, email with image will put extra loading on the email server, which will make the processing time longer. Second, some email servers will mark those "image only" emails as junk mails or spam mails. This, of course, will lower the chance to deliver the mail to your customer.
2. No attachment
Similar to the above case, emails with attachment will put extra loading on the email server. Under the threat of virus, some email servers will filter out the email attachment. The customer may not get what you want to provide. Also, nowsaday, most users are very sensitive to those unknown email attachments and they will not take risk to open the attachment.
3. No fancy HTML email
HTML email can provide a feature rich interface. However, not all email clients support the HTML email well. Even the email clients claim they are support HTML email, different email clients performs differently. If the email clients cannot support well, how can your customer read the message? Moreover, many users set the email client as "Do not load image automatically", your email will have many blank areas in this case.
4. Write down recipient's name
This will raise the customers' interest because they don't want to skip any message that related to them.
5. Provide your sender address
Some email server will block those emails with invalid sender address, or emails' sender address that not exists in the recipients' address book. So don't hide your name, let your customer knows who you are.
