Brandwave

Spark vs Thunderbird:Which is more popular?

In September 2026, Spark had more branded searches than Thunderbird among email clients worldwide. Spark had about 40,500 branded searches, while Thunderbird had 29,100. Spark made up 36% of all email client searches we track, and Thunderbird accounted for 25.9%. When we asked ChatGPT and Google AI Overviews about email clients, Spark and Thunderbird each appeared in four of the five answers. Thunderbird was mentioned before Spark in three out of five answers.

Among email clients worldwide in September 2026

Who do people search for more?

Spark, about 39% more searches than Thunderbird

Spark 40.5K searchesThunderbird 29.1K searches

Who does AI mention more?

Both were mentioned in 4 of 5 answers.

Spark in 4 of 5Thunderbird in 4 of 5

Who does AI recommend more?

Thunderbird, named ahead of Spark in 3 of 5 answers

Thunderbird first in 3Spark first in 2

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Top email clients in ChatGPT and Google AI Overviews

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

Most recommended by AI

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

  1. Spark1st
  2. Thunderbird2nd
  3. Proton Mail3rd
  4. Superhuman4th
  5. Airmail–
  6. Newton–

Mentioned by AI

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

  • 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 Spark or Thunderbird more popular in search?

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

Spark and Thunderbird among email clients worldwide, by month

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

View monthly share of searches table
MonthSparkThunderbirdSuperhumanAirmailNewtonProton Mail
Oct 202523.5%36.1%20.2%19.3%0.76%0.12%
Nov 202521.6%34.5%25.1%17.7%0.97%0.14%
Dec 202520.2%34%23.8%20.3%1.5%0.13%
Jan 202618.6%38.3%26.8%15.3%0.84%0.14%
Feb 202614.6%39%33.3%12%0.99%0.17%
Mar 202615.6%36.5%34.1%12.8%0.76%0.18%
Apr 202615.6%36.5%33.5%12.8%1.4%0.15%
May 202616.8%34.7%36.4%11.3%0.67%0.16%
Jun 202621.4%29.6%27.7%17.6%3.5%0.2%
Jul 202620.7%35%29.1%13.9%1.1%0.24%
Aug 202622%35.2%23.7%18.1%0.71%0.26%
Sep 202636%25.9%24%13.2%0.64%0.28%

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

3 findings
  • The lead changed hands once in the 12 months ending September 2026: Spark took it in September 2026.
  • Across the 12 months ending September 2026, Spark’s share of searches among email clients worldwide moved from 23.5% to 36%, and its estimated monthly branded searches moved from 27.1K to 40.5K.
  • Across the 12 months ending September 2026, Thunderbird’s share of searches among email clients worldwide moved from 36.1% to 25.9%, 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?

2 changes

  1. In September 2026, Spark overtook Thunderbird and Superhuman to become the leader among email clients worldwide, with 36% of the searches.

  2. In September 2026, Thunderbird lost share of searches among email clients worldwide, from 35.2% to 25.9%.

How are branded searches counted?

4 search terms

Brandwave collects information about searches that people make online using Spark’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.

Spark

1 branded search term

  • spark email

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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