Email is so fast and cheap that you can be tempted not to worry about this stuff. But, rather than spend time and money improving deliverability, why not just go for the spray-and-pray approach to email marketing?
If you don't focus on deliverability, you'll run into some severe problems, such as:
YOUR EMAIL COSTS GO UP
Email is a very cheap method of communication, but it is not free. Most associations use an email automation service that charges on a per-send basis, so every email counts. Focusing on the rules of deliverability will help cut down on wasted emails.
YOUR SENDER REPUTATION SUFFERS
There's no system of appeal for your sender's reputation. It's based entirely on the quality of previous emails sent, which means that when you send garbage, your score plummets, and there's nothing you can do about it.
YOU'LL BE ADDED TO BLACKLISTS
Blacklisting is the worst-case scenario. It means that anything you send will be automatically rejected, cutting you off entirely from all recipients at that domain. You might be able to convince the email server administrator to remove you from a blacklist manually, but that's entirely at their discretion.
PEOPLE WHO WANT YOUR EMAILS WON'T GET THEM
Deliverability generally works on a per-domain basis. If one person at that domain flags you as spam, it will affect inbox placement for everyone at that domain.
For example, imagine that Donna and Larry work together at Omnicorp Ltd. Donna is an existing association member, while Larry is a potential lead. You bombard larry@omnicorp.com with lots of poor-quality marketing emails, which he flags as spam. Eventually, the omnicorp.com email server will start blocking all messages from you – which means that donna@omnicorp.com won't get her newsletters or other vital member communications.
Maximizing email deliverability isn't hard. It's just a matter of following best practices – authenticate your domain, maintain your distribution lists, and send great emails.