Avoid words that trigger spam
Do not include spam tainted words in your email "subject line" and in the “email body”. As preventive steps, run the email template through the spam checker. This will help you weed out inadvertent usage of spam words. Another way to keep you updated on new words is by tracking and avoiding words that appear in junk filter list of Microsoft Outlook’s junk filter or in the third party email clients.
Some of the common words that spam filters include are:
Free!,$$$,50% off!, click here, call now!, subscribe, earn $, discount!, online marketing, order now, please read, don't delete, etc.
Use a consistent “From” field
Use a consistent sender in all outgoing emails. Use your brand name, not an anonymous name, in the "from" field. Moreover, consistent messaging policy enables you to meet the right expectations of the recipients and help you to maintain good relations with ISPs.
Don’t mail to someone if they have unsubscribed. As a good practice, group the unsubscribe and remove them within 10 days of the request. Failure to remove opt-outs will result in user complaint. Too many complaints will attract the attention of ISPs and in turn their filters will stop your mail from traversing. Due to such serious retribution, most email vendors ensure that opt-outs are automatically removed from the database.
Keep HTML formats Simple
Here are 3 elements in HTML to avoid:
1. Avoid HTML table with a thick border
3. Avoid making HTML code harder to understand in decompiled form