Many members don't open email because of the Sender name, the Subject Line or both. And the Sender name is as important, if not more important, than the Subject Line.
1. Use a known name as the Sender. Don't create a new generic sender name (or new domain name) for something you may urgently need your members to read - such as comments@, noreply@, etc. If the user has never heard of that Sender, there's increased potential it won't be opened. If you can use the name of a person who has credibility (president, CEO, company owner) it will increase open and response rates.
2. Have a known way to identify it's from your organization. Many email messages I receive that want me to do something (like respond to a legislative call to action) don't make it clear who the message is from - or that there's any urgency. Assuming your organization has a name or acronym, use it somewhere in the subject line to show it's from you. If possible, be consistent with how you identify messages from your organization. Subject lines like "look what they're doing now" read like spam.
3. Members don't know legislative bill numbers. Seriously, stop using numbers in your Subject Lines. Unless all the recipients are on your legislative committee or deeply involved in politics, adding a bill number to a subject line is going to be totally meaningless to the recipient.
4. Tell them it's coming, tell them how to find it if they missed it. If you're sending something important - like a survey, important update, call to action - tell the members it's coming and when to expect it. After you send it - tell the members how to find it every way you can (Twitter, Facebook, login, web site, etc.) -- i.e., what the name of the Sender and what the Subject Line was - so they can find it in their mail file. Or, tell them where else that info might be located (if there's somewhere else).
5. Assume they're reading your message on a mobile device. Send your own message to you and see how easy it is to read on mobile. If you've bombarded an otherwise readable message with too many graphics and attachments, rethink how you communicate by email.
Remember, it's the Sender and the Subject Line that will determine what is opened.