An analysis in the WhatCounts blog points out that sending newsletters on Tuesday is a better idea than sending them on Thursdays.
The reason? People read much less emails on the weekend. What does weekend have to do with sending on Thursday? Email open rate decay.
Email open rate decay means how quickly does a mailing lose its influence and stop being opened. Not everybody reads your email the day you send it.
What they discovered is that when they send their newsletter on a Tuesday, the email open rate decay is much smoother compared to Thursday. On the weekend there’s a drastic dropoff in opens.
The difference in the overall open rates was 5% (same subject line, same content). How much that 5% matters depends on your list size.
So send on Tuesdays.