There are many guidelines available oneline to help your bulk email campaign. Following are some of the tips that help you while sending mass email to your customes. The list is not limited to the below points, but we can find out other tips on other blog posts of this site.
1) All bulk messages you send must be formatted according to RFC 2822 SMTP standards and, if using HTML, w3.org standards.
2) Messages should indicate that they are bulk mail, using the 'Precedence: bulk' header field.
3) Attempts to hide the true sender of the message or the true landing page for any web links in the message may result in nondelivery.
4) The subject of each message should be relevant to the body's content and not be misleading.