Brandwave

Microsoft Outlook vs Thunderbird:Which is more popular?

In September 2026, Microsoft Outlook had more branded searches than Thunderbird among email clients worldwide. Microsoft Outlook had about 1.2 million branded searches, while Thunderbird had 29,100. Microsoft Outlook made up 83.1% of all email client searches we track, and Thunderbird accounted for 2%. When we asked ChatGPT and Google AI Overviews about email clients, Microsoft Outlook appeared in all five answers and Thunderbird in four. Microsoft Outlook was mentioned before Thunderbird in four out of five answers.

Among email clients worldwide in September 2026

Who do people search for more?

Microsoft Outlook, about 42 searches for every 1 for Thunderbird

Microsoft Outlook 1.2M searchesThunderbird 29.1K searches

Who does AI mention more?

Microsoft Outlook, mentioned in every answer we collected

Microsoft Outlook in 5 of 5Thunderbird in 4 of 5

Who does AI recommend more?

Microsoft Outlook, named ahead of Thunderbird in 4 of 5 answers

Microsoft Outlook first in 4Thunderbird first in 1

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Top email clients in ChatGPT and Google AI Overviews

In three ChatGPT questions and two Google AI Overviews, Microsoft Outlook appeared in all five answers. Thunderbird was mentioned in four out of five: in all three ChatGPT answers and in one of the two Google AI Overviews. Microsoft Outlook was listed before Thunderbird in four out of five answers.

Most recommended by AI

Brands get a higher ranking if they are mentioned earlier in the answers.

  1. Microsoft Outlook1st
  2. Apple Mail2nd
  3. Thunderbird3rd
  4. Spark4th
  5. Proton Mail5th
  6. Superhuman6th
  7. Airmail–
  8. Newton–

Mentioned by AI

Each dot is one answer, filled in when that answer mentions the brand.

  • Microsoft Outlook5 of 5Named in 3 of 3 ChatGPT answersNamed in 2 of 2 Google answers
  • Apple Mail5 of 5Named in 3 of 3 ChatGPT answersNamed in 2 of 2 Google answers
  • Spark4 of 5Named in 2 of 3 ChatGPT answersNamed in 2 of 2 Google answers
  • Thunderbird4 of 5Named in 3 of 3 ChatGPT answersNamed in 1 of 2 Google answers
  • Superhuman3 of 5Named in 2 of 3 ChatGPT answersNamed in 1 of 2 Google answers
  • Proton Mail3 of 5Named in 2 of 3 ChatGPT answersNamed in 1 of 2 Google answers
  • Airmail0 of 5Named in 0 of 3 ChatGPT answersNamed in 0 of 2 Google answers
  • Newton0 of 5Named in 0 of 3 ChatGPT answersNamed in 0 of 2 Google answers

See every answer about email clients

5 answers

Not named in any answer:

Brands are shown in the order each answer named them. The survey took place in the United States on October 20, 2026.

Is Microsoft Outlook or Thunderbird more popular in search?

This chart shows how often people search Google for Microsoft Outlook and Thunderbird by name. Each line represents a brand's share of searches for all eight email clients we track, month by month, from English-language searches worldwide.

Microsoft Outlook and Thunderbird among email clients worldwide, by month

Share of searches by month for Microsoft Outlook, Thunderbird. The figures are in the table below the chart.

View monthly share of searches table
MonthMicrosoft OutlookApple MailSparkThunderbirdSuperhumanAirmailNewtonProton Mail
Oct 202586.7%7.8%1.3%2%1.1%1.1%0.04%<0.01%
Nov 202584.8%9.3%1.3%2%1.5%1%0.06%<0.01%
Dec 202581.6%11%1.5%2.5%1.7%1.5%0.11%<0.01%
Jan 202684.1%9.2%1.2%2.6%1.8%1%0.06%<0.01%
Feb 202686.4%7.8%0.85%2.3%1.9%0.7%0.06%<0.01%
Mar 202685.7%7.7%1%2.4%2.3%0.85%0.05%0.01%
Apr 202684.4%7.6%1.3%2.9%2.7%1%0.11%0.01%
May 202684.9%7.7%1.3%2.6%2.7%0.85%0.05%0.01%
Jun 202685.1%7.7%1.5%2.1%2%1.3%0.25%0.01%
Jul 202683.5%9.2%1.5%2.6%2.1%1%0.08%0.02%
Aug 202683.8%9.3%1.5%2.4%1.6%1.3%0.05%0.02%
Sep 202683.1%9.2%2.8%2%1.8%1%0.05%0.02%

How has the Microsoft Outlook and Thunderbird comparison changed over the last 12 months?

3 findings
  • Microsoft Outlook was ahead of Thunderbird in every measured month of the 12 months ending September 2026.
  • Across the 12 months ending September 2026, Microsoft Outlook’s share of searches among email clients worldwide moved from 86.7% to 83.1%, and its estimated monthly branded searches moved from 1.8M to 1.2M.
  • Across the 12 months ending September 2026, Thunderbird’s share of searches among email clients worldwide held steady at 2%, and its estimated monthly branded searches moved from 41.6K to 29.1K.

How did search popularity change for email clients worldwide in September 2026?

3 changes

  1. In September 2026, Spark overtook Thunderbird and Superhuman to rank 3rd among email clients worldwide, with 2.8% of the searches.

  2. In September 2026, Microsoft Outlook lost share of searches among email clients worldwide, from 83.8% to 83.1%.

  3. Estimated monthly branded searches for Thunderbird worldwide fell 30% over 12 measured months, from 41.6K to 29.1K in September 2026.

How are branded searches counted?

4 search terms

Brandwave collects information about searches that people make online using Microsoft Outlook’s and Thunderbird’s names. When viewed over time, estimated search volumes for these branded terms can be used to understand whether interest in the brands is growing, holding steady, or fading.

Microsoft Outlook

1 branded search term

  • microsoft outlook

Thunderbird

3 branded search terms

  • thunderbird client
  • thunderbird email
  • thunderbird email client

How the Brand Demand Index is measured

Other head-to-heads among email clients

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