Where can I obtain information on my Reserves promotions and discharge?

IF you ever established a DS Logon account, then you can access you iPERMs records online* or through the HRC My Records portal* (if not, follow the prompts at DS Logon).

If there is nothing there, then you can access the Defense Personnel Records Information Retrieval System (DPRIS) (again, using a DS Logon account or setting up the new MyAuth account) and use it to request your personnel file. Much faster than 'snail-mail'
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* iPERMS online - https://iperms.hrc.army.mil/login/
* HRC My Records - https://www.hrcapps.army.mil/portal/
* DPRIS request - https://milconnect.dmdc.osd.mil/milconnect/protected/portlet/dpris

I don't recall ever getting a letter from the president but I did generated form letters.

The video is more informative.
To request records from the Army Reserve in St. Louis, you need to contact the National Personnel Records Center (NPRC). You can mail or fax a signed and dated request to the NPRC at:
National Personnel Records Center
Military Personnel Records
One Archives Drive
St. Louis, MO 63138
You can also fax your request to [login to see] .
Please ensure your request includes all necessary identifying information, such as your full name, service number, and date of birth, to help them locate your records.
COL Randall C. SMSgt Lawrence McCarter