# Thunderbird 155.0 — Thunderbird 155.0

- Product: Thunderbird (https://whatsnew.fyi/product/thunderbird)
- Vendor: MZLA Technologies
- Date: 2026-09-01
- Version: 155.0
- Original notes: https://www.thunderbird.net/en-US/thunderbird/155.0/releasenotes/
- Permalink: https://whatsnew.fyi/product/thunderbird/releases/155.0
- Labels: Platforms: Desktop

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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What’s New S/MIME popup shows signature, digest, encryption algorithms and key sizes Default address book for manually added contacts configurable with mail.addr_book.add_item_default_uri Enterprise p…

- **added** — S/MIME popup shows signature, digest, encryption algorithms and key sizes
- **changed** — Default address book for manually added contacts is now configurable with mail.addr_book.add_item_default_uri