As of 2 October 2026. A message was sent but is missing from Sent? Do not immediately send it again: transmission and saving a copy need separate checks. This guide is for home users and small offices using Thunderbird Desktop with an IMAP account.
What version 157 actually fixes
The Thunderbird 157.0 release notes dated 30 September 2026 list a fix for sent messages silently failing to save to the IMAP Sent folder. [1] This does not establish the cause of every missing copy, or whether an ESR version is affected or fixed. Updating is not evidence that previously missing messages will be recovered.
Preparation
Record the version, update channel, operating system, account type and time of the problem. Note the existing destination under Account Settings → Copies & Folders; labels may vary. Before making changes, close Thunderbird and copy the profile to a separate protected location, also backing up separately configured message stores. The copy can contain private data and credentials: do not attach it to a support ticket. [2]
Six safe checks
- Check the existing send: search by subject, time and recipient in Thunderbird and webmail for the same account. Include alternative Sent folders and Local Folders. A missing copy does not prove failed delivery; conversely, a Sent copy does not prove delivery to the recipient. Do not resend work messages as a precaution.
- Inspect the destination: open Copies & Folders for the sending account or identity actually used. Check whether a copy should be saved and which exact folder is selected. Local storage does not automatically appear in webmail. The option for replies can store copies in the original message’s folder. [3] Do not change settings speculatively.
- Separate server state from display: if the copy exists in webmail but is not visible locally, temporarily clear search/Quick Filter restrictions and check the correct folder. Visibility and offline synchronization are different matters. [4] If it is also absent in webmail, record that finding; it does not by itself prove the release bug.
- Update appropriately: after backing up, use the existing installation or IT deployment route and complete the restart. About Thunderbird checks for updates for directly installed versions; do not bypass package management or company policies. [5] 157.0 is the documented Release-channel fix here, not an instruction to downgrade or switch from ESR.
- Run a controlled test: if permitted, send exactly one harmless message with a distinctive subject to a second address you own. Use no confidential content. Check receipt separately from the copy in the intended Sent folder, then find that same copy in webmail. Do not keep sending when the result is unclear.
- Record the outcome: note version, sender identity, destination folder, time and both results. Restart Thunderbird normally and reopen the copy. If the failure persists, give your provider or IT the sanitized error and observations, without passwords, complete profiles or private messages.
Interpret the result and keep a way back
Success here means the controlled message reaches your own destination and its copy remains visible in the intended folder and, for server-side IMAP storage, webmail. One successful test does not guarantee every account works. For duplicate copies, clarify the provider’s saving rules before deleting anything. Revert only a deliberately changed folder mapping using your notes; do not remove accounts, delete index files or open a working profile with an older version. Before a necessary restore, also preserve the current state and involve IT.
Sources and limitations
Source-based editorial diagnosis, not a hands-on Thunderbird or mail-sending test. No affiliate links or paid repair tool are needed. The rationale is a current developer notice, not a demonstrated search surge for this fault.