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Things to keep in mind when using custom HTML in Gmail ads!

Gmail native ads will be released to the public on September 1st, and some of you may already be using them. 

In Gmail ads, in addition to template ads prepared in advance by AdWords, it is also possible to use HTML created by the operator as an advertisement (custom HTML). When I created some Gmail ads with this custom HTML, I tried to summarize the points I was concerned about and the points I had to be careful about.

Gmail ad performance

How are Gmail ads performing? I think it’s a lot of people who think. In conclusion, my impression is that it can appeal a lot of information at a fairly low unit price, similar to Youtube’s TrueView advertisement . Furthermore, as a targeting setting unique to Gmail advertisements, it is also possible to display advertisements to users who receive emails from the specified domain .

The performance of Gmail ads created in a hurry by slightly resizing the banners used for normal display ads is as follows.

impressions Number of advertisements deployed Advertising rate Advertising unit price Number of transitions to website number of transfers number of saves
40,229 4,460 11.09% ¥7 30 8 twenty five

It is, and the advertisement is expanded more than expected. I think the number of transitions to the website, the number of transfers, and the number of saves are a little small, but I think there are parts that lack appeal because they were created in a hurry. Currently, we are experimenting with custom HTML ads that extract some elements from the information on the landing page, so we think that the numbers for “transitions to the website”, “transfers”, and “saves” will improve. will be split.

Also, looking at the distribution ratio by device, although there is not a big difference between PCs and smartphones in terms of the number of impressions, the click rate on smartphones is extremely high, so we believe that it is essential to create a smartphone version of the landing page. can be

Benefits of using custom HTML

First of all, the cost for advertisement development is very low, and by creating a page with custom HTML, it is possible to put a lot of information in the developed advertisement, increasing the appeal. Also, if you make full use of the ad size limit, you can use a size of 650px wide and 1,000px high, so you can compose it as a kind of landing page. On top of that, it is also possible to land directly on the inquiry form and document request form from the advertisement, and if only the email address is registered, the form can be placed directly in the custom HTML. In addition to transitioning to the form, it is also possible to set up multiple links to the website for those who want to know more about other points.

For that reason, custom HTML mail that has been properly crafted can display advertisements with a large amount of information and strong appeal, and furthermore, it is an advertisement that can keep the information transmission cost (cost per click) low.

Conventions for Custom HTML

Custom HTML conventions are basically:

Although it is summarized in , I will describe it just in case.

  1. HTML file must contain at least 1 image (but no more than 100 images)
  2. Include at least one URL that transitions to an external site (however, it must be within a maximum of 15)
  3. The size of the HTML should be a maximum width of 650px and a maximum height of 1,000px (however, it is recommended that the height be less than 650px).
  4. No remarketing tags or conversion tags can be placed in HTML, nor can other external resources be used.
  5. All CSS to be used should be described using style attributes for tags. Also, the types of CSS that can be used are limited.
  6. JavaScript is not available
  7. Flash, HTML5, voice functions, iframes, and animated images are all prohibited
  8. All encoding is UTF-8

The second half of the rules is about the HTML mail itself, so I think there is no problem, but the first half is the point. However, I think that there is no problem except for the limit of the number of transition URLs to external sites and the size of HTML.

Precautions when preparing custom HTML

Constraints in available technology

At first, I overlooked the specification that HTML5 cannot be used, and coded HTML using the <section> tag, <main>, <header>, and <footer> tags newly introduced in HTML5. And the error message is not something like “HTML5 tags cannot be used”, but after deleting all the tags set under these tags introduced in HTML5, error checking is performed, As a result, “There is no URL in the HTML that transitions to an external site”. In the coded HTML, I had created about 6 URLs to transition to external sites, so it took me a long time to find the cause.

In this way, it may be difficult to “find the essential issue” from the “error message”.

Pitfalls of teaser.txt

Thanks to the help feedback, the pitfalls of teaser.txt have been resolved. It’s okay to think about something like this in the past.

As the Display Specs help says,

広告主: サンプル広告
見出し: サンプル メッセージ広告
説明: メッセージ広告のサンプル テキスト
表示 URL:
ランディング ページ:

I created teaser.txt in such a way, but it says that “advertiser”, “headline”, “description”, “display URL” and “landing page” are not specified.

I think that many people get stuck in this, but this Display Specs page and even the item names have been translated . Correctly,

Subject:サンプル メッセージ広告
Description:メッセージ広告のサンプル テキスト
Landing page:

I have to. Since I am sending feedback from AdWords help, I think that the help page will be corrected at some time (or the AdWords side will be corrected so that the translated item name will not be an error), but I am not sure when it is implemented. must be turned on.

In addition, the error message is not refined yet, and it is possible that you tried to register, but an error occurred and you could not avoid it. For example, the error message “The line is too long” indicates that the number of characters in the advertiser, headline, and description fields set in teaser.txt exceeds the specified number of characters, but the error message is difficult to understand. , the problem may be difficult to identify.

For these reasons, it seems necessary to submit the manuscript with plenty of time to spare.

Pitfalls when generating zip files

This is also written in the help, so there may be few people who fit in, but when you create a ZIP file, compress it so that index.html and teaser.txt exist directly under the ZIP. If you zip the folder containing index.html and teaser.txt, you will be told that the index.html and teaser.txt files cannot be found. Compressing as in the capture below is the correct way to do it (same for Windows).


Until now, I think that banner images were the main focus of display advertising, but creatives themselves are spreading from images to HTML and JavaScript, such as rich media and light boxes. And considering the possibility of custom HTML ads in Gmail ads, it seems that advertising operators will need to know not only about operation but also about fields such as creative and HTML production in the future.


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