How does Piano ESP search for duplicate stories from previously sent emails
Duplicate articles in the email campaigns are typically caused by changes to the existing articles in your RSS feed.
The following are important tags in your RSS feed:
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<guid>: article's unique ID
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<title>: article title
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<category>: article category
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<link>: link to the article
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<description>: short summary or full text of the article, depending on your needs
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<pubdate>: date of publication
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<date>: when article was added to the RSS feed
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<enclosure>: description of an object that is attached to the article (usually includes a link to an image)
In case you alter the <title> of an existing article, then the story's <link> may automatically change as well. If this story doesn't have a <guid> in the RSS feed, Piano ESP will recognize this as a new story, so our content recommendation engine may send two similar articles. In addition, if you change the story's <link> with unspecified <guid> tag, Piano ESP will consider it a new article and may send two copies.
<guid> - it is an optional tag used as the article's ID. If the story does not contain <guid> tag in the RSS feed, our system uses <link> tag to identify the article. If <guid> wasn't specified in the feed and the <link> tag was changed, then our system will consider the story as a new one.
To prevent sending duplicate articles, we also recommend having a <guid> tag in your RSS feed, which would reliably identify the article despite any changes made to other tags.
If you make any changes to your existing article, you must update the <date> tag. If you do not have a <date> tag, update the <pubdate> tag.
And also, while Piano ESP searches for duplicate stories, the content recommendation engine looks back no more than 4 previous emails sent to the user that are not older than 30 days (considering all email campaigns).
So if you sent out more emails in a short period of time the Piano ESP may re-pick some articles that have been sent recently (e.g. in case you want to send out more than 4 emails per day the chances that duplicate articles will be picked are high).
Responsible for this logic is Exclude stories sent previously setting which lives in Dynamic block settings. By default, this option is enabled.
In addition to that, please note, that ESP does not check duplicates for such stories that were added more than 45 days ago. Therefore, we recommend avoiding situations of adding articles that duplicate the content of old articles (added more than 45 days ago), because our system simply will not match such duplicates.