We have had a longstanding intermittent problem that is gradually getting worse. When sending emails the outgoing SMTP sending happens quickly, but there are massive delays in saving the sent message to IMAP folders. Often it can take well over 1minute to save a message and quite often it does not save at all eventually we get a timeout with the error "Your message has been sent but a copy cannot be saved". I appreciate there is the option to save to a local folder but it is a real pain to have to use this all the time. This delays are happening across several different email accounts hosted with more than one ISP and whilst it is an intermittent problem it is occurring more than 50% of the time across multiple PCs. Note: We use the option "Place replies in the folder of the message being replied to". However, the problem also arises with new outgoing messages that are not replies that would just be saved in the "Sent" folder. We are using Thunderbird 115.1.1 (64-bit) running on Windows desktop PCs and laptops. I have contacted the ISPs concerned but they think it is nothing to do with them and suggest it is an issue with Thunderbird. I see this has been reported by other Thunderbird users, but the help resposes do not seem to offer a definitive solution. If it really is a problem with the ISP's IMAP hosting, please advise how I can gather evidence to convince the ISPs that they have a server problem. Our broadband speed is good and there are no significant delays with any other internet activity. Thanks.