Not all users who open an email think in the same way, nor are they equally receptive to the different messages they may encounter. Associating the subject of an email with the objective of getting openings is a mistake that many people make and that we must try to avoid . The main objective of an email, whatever part it is, is to get users receptive to the call to action in order to obtain conversions. And that means transmitting in the subject exactly what the user will find in the email. In a more or less original way, but always faithful to the content of the email. In this way we will avoid many disappointments.
The goal of the subject line is not to generate opens. The real goal of the subject line is to generate openers that are likely to convert.
The myth “to measure the effectiveness of your accounting directors email lists subject lines, look at the open rate” no longer holds true. The open rate can tell us which subject line is most likely to lead to an open, but it says nothing about what happens once that email is opened. And as we have said, the goal is not the open per se, but the conversion, so this metric only gives us a small part of the information.
The subject line is an element that offers many possibilities and one of them is the opportunity for subscribers to self-segment their inbox . What does that mean? That, by reading the subject line, the user is able to see if that email is the right one for them or if it doesn't contain anything that might interest them, so that the user really knows how to select from their inbox only what really interests them. Many of you will think, but then, we lose the chances of them opening our emails. Probably. But it is better for them to be opened by a few users who are likely to convert, than by many users who are not interested in what you have to say.

The key is not to waste your users' time. There are different tips that can help you make the subject more original or make it more attractive. But don't forget that clarity and detail are the best way to reach your ideal target. Trying to get openings at all costs will be useless if what you want is to focus on creating a relationship with the subscribers of the database and providing them with everything they are looking for.
How can we measure the effectiveness of email subjects?
By doing A/B testing and looking at variables such as:
Open Rate
Clicks Rate
Click-to-open Rate
Conversion Rate
Each of these metrics has a different purpose. Analyzing all 4 metrics will give you a more complete view of the effect your email subjects may be having on users. Don't just focus on openings. If you do, you'll miss out on capturing the real effectiveness of your emails. If a user opens your email but doesn't convert, we don't necessarily consider that subject to be appropriate for that email. The subject must be in line with the objective you're looking for and therefore, it must seek conversion .