Overview
The success of your email campaigns is dependent on whether messages end up in the inbox vs. the spam folder. It's called deliverability: how many of your messages actually get delivered into the inbox? Email account providers have put in place all sorts of filters to block unsolicited email messages (rightfully so!). You need to make sure that your campaigns are not mistaken for unsolicited messages and placed in the junk folder.
Your deliverability depends mostly on your reputation as a sender. That's a value that you can measure, monitor, and improve over time.
Your reputation is at the "account" level (vs. "list" level) and mostly depends on:
- percentage of messages that bounce back (bounces)
- recipients' behavior (opens, clicks, spam compliants, etc.)
- list hygiene (how recipients are collected, how unsubscribes are handled, etc.)
What's the impact of having a low reputation?
Your reputation has a major impact on your deliverability. It affects all messages sent from the same account (i.e. it affects all lists).
Your reputation as a sender is directly linked (and a good indicator of) the level of engagement of your recipients (how much do they open and click?). More and more email account providers (e.g. Yahoo!, Gmail, Outlook.com, AOL, etc.) use "engagement" as a fundamental part of their inboxing algorithms (i.e. the formulas they use to determine whether your message should be "inboxed" or "junked").
Developing a high level of engagement can take some time, and you need to be careful: a false step (e.g. sending a message that seems unsolicited) could back-fire and nullify all of your hard work.
Reputation vs. Message content