The first things that email filters look at when you are going to send out an email, is the content of the subject line, if they find words they considered to be "spammy", they will sure block your emails.
Every time you are going to send out a blast you have to consider the fact that the subject line is not only the first thing your recipient will see, but also, it is one of the most important factors that will decide if they will open what you are sending to them, or if they will not.
Good subject lines have to be simple, clear and to the point. If the recipient is interested in what you are sending them, they will be very happy if your subject line directs them to what the email will be about.
Always make sure that when trying to sell a product, you do not make your recipients feel pressured. That will prevent them from opening your emails.
A subject line that should be avoided is one that makes the recipient feel that they are being pushed to buy something. Recipients should always feel that they have different options, and that you are informing them but not obligating them to buy anything.
Avoid exclamation signs, they tend to make recipients feel that they are being pushed to buy something. Avoid ALL CAPITAL letters, it makes clients feel that you are screaming at them. A good subject line should never be caught by spam filters that is why it is also wise to avoid words such as free, mortgage, money, etc.
Always read the subject line before sending out the email and make sure it sounds good and appropriate, and has no grammatical and spelling errors.