[MlMt] Duplicate messages in Sent Items (Exchange account)

[Bill Cole]

On 2026-03-03 at 11:29:33 UTC-0500 (Tue, 3 Mar 2026 16:29:33 +0000)
Henry Seiden <mailmate at lists.freron.com>
is rumored to have said:

> If it has been the case this long, pretty sure Benny, the developer 
> has known about it as has M$ (Microsoft).

Benny knows A LOT. Unfortunately, not enough people pay for MM to 
support him hiring help, or at least that is the impression I've gotten.

Microsoft knows NOTHING about 3rd-party mail clients. They don't care, 
except when given an opportunity to degrade the experience of using 
non-MS software.

> As to why they each made that conscious decision is up to the 
> respective developers, I’m betting it was a conscious one on each of 
> them. Mailmate shouldn’t be responsible for unique non-standard 
> server’s, that’s a slippery slope in my opinion.

Agreed. It's an easy workaround for those cursed with Exchange to either 
ignore the dupes or use a MM rule to hide them.

I *thought* that Benny had provided a new 'defaults' pref to disable 
saving a copy of sent messages to the Sent mailbox, but I can find no 
such conversation now...

> It is easily avoidable on the users’ end, regardless.

I'm sure a rule could do the trick.

It may be possible in MailMate to create a second mailbox for sent 
messages, tell MM that it is the special "Sent Messages" mailbox 
("mailbox type" contextual pull-down) and then just unsubscribe from the 
place Exchange is putting copies. I HAVE NOT TESTED THAT!

> On 3 Mar 2026, at 11:21, aisrael wrote:
>
>> I am not sure if it helps, but I found this message from 2022 
>> (however it seems the raw headers of the pairs of mails were 
>> different in the reported case, which may not be your case)  :
>>
>> This is a known issue: Mailmate moves the message from Drafts to Sent 
>> after you send it (that's the one with few headers), and then 
>> Exchange "helpfully" puts a copy of all outgoing mail into Sent as 
>> well. I have simply made a smart "In/Out" mailbox to show me messages 
>> where "From is not me" or "Received does not exist", which hides all 
>> of the Exchange copies.
>>
>> Alain
>>
>> On 3 Mar 2026, at 16:48, Jeff Bullard via mailmate wrote:
>>
>>> I appreciate the response and that this is a cosmetic issue and not 
>>> an operational problem. Even so, I think the developer should be 
>>> able and willing to investigate and fix this, especially since the 
>>> duplicates do not appear within any other email client I have on my 
>>> computer (Apple Mail, Outlook, and Airmail).  It those apps all 
>>> figured it out, why not MailMate? Just saying it “is a known issue 
>>> and can be ignored” is not a very helpful response for those of us 
>>> who are experiencing it, especially since (a) Exchange is an 
>>> extremely common mail server and (b) some of us did pay at least a 
>>> small amount for MailMate.
>>>
>>> Jeffrey W Bullard PhD | FACerS | FWAS
>>> Department of Materials Science and Engineering
>>> Zachry Department of Civil and Environmental Engineering
>>> Texas A&M University
>>> 3136 TAMU
>>> College Station, Texas 77843
>>>
>>> On 3 Mar 2026, at 9:37, Robert Brenstein wrote:
>>>
>>>> This is a known issue and it has been discussed on this list a 
>>>> number of times. As far as I remember, the duplication is caused by 
>>>> Exchange server due to the way it handles sending mail. You can 
>>>> just ignore this duplication. Mail was sent only once. If you 
>>>> search past posts in the list, you may find how others go about 
>>>> this.
>>>>
>>>> On 3 Mar 2026, at 14:45, Luís Trevisan wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> I'm experiencing duplicate messages in my Sent Items folder in 
>>>>> Microsoft 365 / Exchange account.
>>>>>
>>>>> Setup details:
>>>>> - Account type: Exchange / Outlook.com (Microsoft 365 corporate)
>>>>> - The duplicates appear exclusively in the Sent Items folder
>>>>> - The duplicate messages are identical
>>>>> - No other folders are affected
>>>>>
>>>>> Has anyone experienced this with an Exchange account and found a 
>>>>> reliable fix?
>>>>>
>>>>> Thank you in advance.
>>>>> Luís
>>>
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>
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  Bill Cole
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