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Unintended recipient getting added to sent email

%3CLINGO-SUB%20id%3D%22lingo-sub-239885%22%20slang%3D%22en-US%22%3EUnintended%20recipient%20getting%20added%20to%20sent%20email%3C%2FLINGO-SUB%3E%3CLINGO-BODY%20id%3D%22lingo-body-239885%22%20slang%3D%22en-US%22%3E%3CP%3EThis%20week%2C%20I%20was%20working%20on%20an%20issue%20that%20caused%20me%26nbsp%3Bto%20scratch%20my%20head.%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3EIssue%20was%2C%20user%20R%20(recipient)%20complained%2C%20that%20he%20started%20to%20receive%20e-mails%20from%20various%20senders%20he%20does%20not%20know%20and%20does%20not%20do%20business%20with.%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3EAfter%20checking%20some%20samples%20of%20e-mails%20from%20the%20sent%20items%20folder%20in%20the%20senders%20mailboxes%2C%20I%20realized%2C%20user%20R%20was%20in%20the%20To%20or%20Cc%20lines%20of%20the%20mails%20that%20were%20sent.%3C%2FP%3E%0A%3CP%3ECertainly%2C%20the%20issue%20happened%20infrequently%20and%20the%20senders%20varied.%26nbsp%3B%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3ESo%2C%20the%20golden%20question%20was%2C%20how%20did%20user%20R%20get%20onto%20the%20To%20or%20Cc%20lines%20on%20those%20mails.%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3ESimilar%20issues%20are%20described%20here%2C%20e.g.%3A%26nbsp%3B%3C%2FP%3E%0A%3CP%3E%3CA%20href%3D%22https%3A%2F%2Fna01.safelinks.protection.outlook.com%2F%3Furl%3Dhttps%253A%252F%252Fsocial.technet.microsoft.com%252FForums%252Flync%252Fen-US%252Ffbd34bb5-442c-46c9-b131-7920b59f4722%252Funintended-recipient-getting-added-to-sent-email%253Fforum%253Doutlook%26amp%3Bdata%3D02%257C01%257C%257C5ef3730e82be4850770608d60e7759b6%257C72f988bf86f141af91ab2d7cd011db47%257C1%257C0%257C636712303096000521%26amp%3Bsdata%3DZr%252FRbv%252FVdbDHhAMHiBlOGzKhY5zcL8HsSQ3XEDvX5rg%253D%26amp%3Breserved%3D0%22%20target%3D%22_blank%22%20rel%3D%22nofollow%20noopener%20noreferrer%20noopener%20noreferrer%22%3Ehttps%3A%2F%2Fsocial.technet.microsoft.com%2FForums%2Flync%2Fen-US%2Ffbd34bb5-442c-46c9-b131-7920b59f4722%2Funintended-recipient-getting-added-to-sent-email%3Fforum%3Doutlook%3C%2FA%3E%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3E%3CA%20href%3D%22https%3A%2F%2Fna01.safelinks.protection.outlook.com%2F%3Furl%3Dhttps%253A%252F%252Fanswers.microsoft.com%252Fen-us%252Fmsoffice%252Fforum%252Fmsoffice_outlook-mso_win10-mso_365hp%252Foutlook-2016-adding-unintended-recipients-to-my%252F18a13af0-e274-4db2-b5cd-5e82029eb2dd%253Fauth%253D1%26amp%3Bdata%3D02%257C01%257C%257C5ef3730e82be4850770608d60e7759b6%257C72f988bf86f141af91ab2d7cd011db47%257C1%257C0%257C636712303096010526%26amp%3Bsdata%3Dvp%252B71Kj5OSiVFWhhjxTGjMHrnG%252FYDB2hEznhrqZ2y6Q%253D%26amp%3Breserved%3D0%22%20target%3D%22_blank%22%20rel%3D%22nofollow%20noopener%20noreferrer%20noopener%20noreferrer%22%3Ehttps%3A%2F%2Fanswers.microsoft.com%2Fen-us%2Fmsoffice%2Fforum%2Fmsoffice_outlook-mso_win10-mso_365hp%2Foutlook-2016-adding-unintended-recipients-to-my%2F18a13af0-e274-4db2-b5cd-5e82029eb2dd%3Fauth%3D1%3C%2FA%3E%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3EThanks%20to%20my%20co-worker%20Rahul%2C%20who%20gave%20me%20the%20hint%20to%20check%20for%20incorrect%20AD%20properties%20of%20the%20recipient%2C%20and%20there%20it%20was%3A%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3EGet-ADUser%20UserR%20-Properties%20*%3C%2FP%3E%0A%3CP%3E%5B%E2%80%A6%5D%3CBR%20%2F%3EObjectClass%20%3A%20user%3CBR%20%2F%3EObjectGUID%20%3A%20cf55f28a-ce78-4078-b9e6-d2326b58257f%3CBR%20%2F%3E%3CSTRONG%3EotherTelephone%20%3A%20%7B%2C%7D%3C%2FSTRONG%3E%3CBR%20%2F%3E%5B%E2%80%A6%5D%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3EThe%20AD%20property%20otherTelephone%20contains%20the%20unexpected%20comma%20character.%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3EThis%20customer%20has%20the%20otherTelephone%20property%20included%20in%20ANR%20resolution%2C%20so%20if%20a%20sender%20in%20Outlook%20mistakenly%20types%20the%20comma%20into%20the%20To%20or%20Cc%20field%2C%20it%20will%20get%20resolved%20against%20User%20Rs%20e-mail%20address.%3CBR%20%2F%3EThis%20totally%20explains%20the%20issue%20where%20the%20recipient%20user%20R%20unexpectedly%20got%20e-mails%20from%20people%20he%20does%20not%20do%20business%20with%20and%20was%20on%20the%20To%20or%20Cc%20lines%20in%20the%20senders%20Sent-Items.%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%3C%2FLINGO-BODY%3E%3CLINGO-LABS%20id%3D%22lingo-labs-239885%22%20slang%3D%22en-US%22%3E%3CLINGO-LABEL%3EExchange%20Server%3C%2FLINGO-LABEL%3E%3CLINGO-LABEL%3EOutlook%3C%2FLINGO-LABEL%3E%3C%2FLINGO-LABS%3E
Frank Plawetzki
Microsoft

This week, I was working on an issue that caused me to scratch my head.

 

Issue was, user R (recipient) complained, that he started to receive e-mails from various senders he does not know and does not do business with.

 

After checking some samples of e-mails from the sent items folder in the senders mailboxes, I realized, user R was in the To or Cc lines of the mails that were sent.

Certainly, the issue happened infrequently and the senders varied. 

 

So, the golden question was, how did user R get onto the To or Cc lines on those mails.

 

Similar issues are described here, e.g.: 

https://social.technet.microsoft.com/Forums/lync/en-US/fbd34bb5-442c-46c9-b131-7920b59f4722/unintend...

 

https://answers.microsoft.com/en-us/msoffice/forum/msoffice_outlook-mso_win10-mso_365hp/outlook-2016...

 

Thanks to my co-worker Rahul, who gave me the hint to check for incorrect AD properties of the recipient, and there it was:

 

Get-ADUser UserR -Properties *

[…]
ObjectClass : user
ObjectGUID : cf55f28a-ce78-4078-b9e6-d2326b58257f
otherTelephone : {,}
[…]

 

The AD property otherTelephone contains the unexpected comma character.

 

This customer has the otherTelephone property included in ANR resolution, so if a sender in Outlook mistakenly types the comma into the To or Cc field, it will get resolved against User Rs e-mail address.
This totally explains the issue where the recipient user R unexpectedly got e-mails from people he does not do business with and was on the To or Cc lines in the senders Sent-Items.

 

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