Some group emails in sent box but not inbox

Question

Every day I send four group emails of approximately 20 people each and I send the emails as a blind copy to them and send it also to myself to check that it went through. Most days everything goes well and everybody gets the email, but twice now only one of those emails has come into my inbox, but all four of them are in my sent box. I cannot figure out what’s going on. I mail these emails from my laptop, but the same situation shows up on my phone and my iPad and online. Can somebody help me?