Should we export all email addresses available at the moment and note the last registration timestamp so the next export can continue from there, export until some predefined time (say, the previous UTC midnight), or just export whatever is available every time and assume the email sender software will handle repeated email addresses?

Also, how rigid are the dates here? Should we do a test export the previous day, just in case?

In T307451#7916583, @Tgr wrote:

Should we export all email addresses available at the moment and note the last registration timestamp so the next export can continue from there

Probably this way is the safest.

export until some predefined time (say, the previous UTC midnight), or just export whatever is available every time and assume the email sender software will handle repeated email addresses?

Mailchimp knows to deduplicate email addresses when importing, but I imagine that these are being set up as separate campaigns, and in that context Mailchimp might not know to only include a specific email once across the series of campaigns.

In T307451#7916584, @Tgr wrote:

Also, how rigid are the dates here? Should we do a test export the previous day, just in case?

My understanding from T303780: Welcome emails: export opted-in users is that it should just be Mondays and Thursdays. We could do a test export on Wednesday to see how it goes.

On mwmaint1002:

mwscript extensions/GrowthExperiments/maintenance/ExportWelcomeSurveyMailingListData.php --wiki=eswiki --debug --from=20220509000000 --to=20220512093322 --output-format=csv > may12.csv

Debug output:

Converting registration timestamps:
        From (exclusive): 20220509000000 -> UID 6550538 (registered: 20220508235823)
        To (inclusive): 20220512093322 -> UID 6554000 (registered: 20220512093251)

The uploaded file is in the private google drive.

@EdErhart-WMF @MMiller_WMF I will let one of you mark this task as resolved. I've shared the Google Drive folder with you two + @Tgr.