Many compliments have been received on how fast thunderbird is, so it's difficult to answer your question. I am not a network guru, but from my own experience, such delays are usually with the individual's internet connections and server loads. That is, the overall issue of speed involves many variables, only one of which is the email client. Today, for example, My Gmail account is slow in sending, but it is normally fast.

I have an ATT broadband connection which today is zooming along at 900+ Mbps both up and down. Very fast, yet my T-bird is so slow. It takes so long to parse my inbox. Is there a T-bird setting somewhere I can flip, to increase efficiency? It was fine for a week or so, but now it's back to tortoise speed.

Sorry, I am not that technically knowledgeable on internet connections. But someone else here may have suggestions. My only other thought is that, despite internet speed, servers may be overloaded at times or undergoing updates. That has happened to me, but may not be relevant to your situation,

I've been having the same problems. It's not the internet - all other apps work fast. But Thunderbird has gotten SO SLOW - and yes, especially when deleting emails, moving from one to the next, etc. I was thinking it was maybe from a windows update? I'm not sure, but it's Terribly frustrating.

I am the original poster on this thread. T-bird was super slow for a couple of days, and then it got better all of a sudden--it might have been a Windows update--they seem to happen pretty often--but I'm not sure. David might be right about overloaded servers, that is plausible. My upload /download speedtests always top 900mbps ever since I switched to AT&T from Comcast, so that part is OK. I was timing my email deletes, and each one took 2 seconds to delete--painful. Big time sink! Better today, knock on wood.

I've been having the same problems. It's not the internet - all other apps work fast. But Thunderbird has gotten SO SLOW - and yes, especially when deleting emails, moving from one to the next, etc. I was thinking it was maybe from a windows update? I'm not sure, but it's Terribly frustrating.

cinda1, please see https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems. Please post a new question at https://support.mozilla.org/en-US/questions/new/thunderbird if you still have trouble after going through that.