One of the great qualities of being an SDR is that you get to constantly try different things.
More than any other role in a company, you are performing A/B testing constantly with your prospects, and getting immediate feedback. The feedback can be anything from high open rates for certain email sequences
to a prospect reaching out to let you know that they like or dislike your messaging, depending on the day.
You are able to constantly implement this feedback and switch things up to get your message across. And you can do it better each time.
Do not be afraid to experiment and conduct A/B testing of your cold email subject lines, varying the targets and wording, to get a clearer picture of what might work best.
And remember, sometimes it truly does depend on the mood of the person receiving that email, something which is entirely out of your control.
So focus on what you can control, and take it from there.