Compacting Outlook 2010 OST results in old emails being re-sent

Not open for further replies.

Thomas Inman

Outlook version
Outlook 2016 32 bit
Email Account (as MS Exchange)
Hello Diane and fellow readers,

I have a customer running outlook 2010, connected to an offsite company exchange server, and I am compacting the OST now. The customer's OST file is 45GB!! Hence compacting is still running as I write this, 18 hours later.

The customer reported to me this morning that she was told people are receiving old emails from her, and I have never heard of compacting an OST causing this to happen.

This customer's Outlook OST is the largest I have seen since Microsoft changed the size limit from 20GB to 50GB.

My questions are, can compacting actually trigger old emails to be re-sent? And, how long should I continue to wait for compacting to complete? Or should I cancel compacting?
compacting the OST
When it is an ost, it's not really necessary to compact it - you can delete it and let outlook resync. If the mailbox is huge and the internet connection slow, you can check the mailbox size online before deciding which route to take...

and no, i have never seen this reset in old emails being sent. it also shouldn't trigger read receipts being sent back - unless you empty deleted items before compacting.

If they are actual messages being resent, i would 1) verify in OWA that sent messages aren't stuck in the outbox and 2) delete the ost.
The user has a 50 down/10 up connection with Comca$t, however I opted to not delete the OST because it's 45GB, and figured that would take a few days to download again.

She is relatively close to the maximum size for an OST, which I believe is 50GB, so I am hoping that her OST will actually shrink in size. I don't think it has ever been compacted before, spanning at least 5 years. She isn't a huge fan of technology, especially when it comes to computers, so I am going the extra mile to help her any way possible.
if it is not erroring for her, then it is 50 GB (2010 started out with a 20GB default, but it was increased in an update) - and you can raise it higher, although microsoft doesn't recommend going too much higher.

Compacting has the potential to reduce it 20%, so you may recover a lot of space. (Outlook is supposed to automatically compact when there is 20% white space - which is harder to hit when the file is huge.)

My ost is 10GB and i deleted it earlier today hoping to fix a problem with rules (it didn't). It took about 2 hours to download from office 365 on a 100mbit connection.
Update: Compacting had not finished after waiting 24 hours, though the progress bar was still moving toward completion (about 80% done on a 45MB OST file). This user needed her machine back asap, so time was up waiting for compacting to completely finish.

What improved significantly was no more spinning wheel mouse pointer waiting on background operations in Outlook 2016. Navigation is quick once again. I did not have an chance to see the resulting file size after letting it compact for that long a time, but I consider this a successful repair based on the user's positive feedback alone.

Regarding the issue mentioned earlier about the user reporting feedback from colleagues that received 'old' emails from her during the compaction: this appears to be a result of duplicates stuck in the Outbox for who knows how long, that were suddenly able to be sent out. I don't think the issue happens as a result of compacting necessarily, but it was a side effect in this user's case. No such problem exists now, and only a few of her colleagues received duplicate old emails - not everyone in her contact list. So, I believe Compacting an OST file is not harmful, but be prepared for the length of time it takes to complete on an unusually large file.
I consider this a successful repair based on the user's positive feedback alone
Absolutely. My guess is there was either a huge email she deleted (into the GB in size) or a ton of little ones that needed cleaned up. Can't really guess on the size based on how long it took for that reason - but i'm expecting it went down a lot - probably close to half, if not more.

It may have been faster to re-sync it - this is one reason why microsoft recommends deleting ost files....
this appears to be a result of duplicates stuck in the Outbox for who knows how long
This may have been a big reason why outlook was so sluggish but they should not have been stuck there to begin with.
I think your guess on the reasons behind the dramatic speedup in Outlook after compacting the OST is correct.

On another customer system, I did this process differently, deleting the OST, and waiting for a full re-sync. His mailbox was not as large (over 20GB), but still took almost 24 hours to download everything. I watched the count as emails came in, and it was through short bursts with long pauses in between that the re-sync slowly finished. That was with an Office 365 Business plan/Exchange mailbox about 12 months ago.

I haven't figured out the rate O365 transfers data, or more specifically, the pattern, but from my own observations, it seems to be a start/wait/start process. This seems strange to me considering Microsoft has virtually unlimited bandwidth.
Not open for further replies.
Similar threads
Thread starter Title Forum Replies Date
J 'Name on the security certificate is invalid or...' - Outlook on desktop talking to account Using accounts in Outlook 4
J Outlook, Word, Access crash unless run in Admin mode - time dependent it seems Using Outlook 8
T Why do Outlook Desktop 2021 tasks from my wife's email show up in my task pane? Using Outlook 2
B Delete Read Receipts in Your Outlook Outlook VBA and Custom Forms 0
M Outlook changes the "Modified" field when moving/copying a Contact. Using Outlook 0
macdotcom Outlook 365 Outlook folder export to PST archival tool - close, but need a nudge Outlook VBA and Custom Forms 2
M Outlook 2016 still feature updating Using Outlook 0
e_a_g_l_e_p_i Question about Outlook 2021 and Gmail Using Outlook 9
J Outlook VBA to send from Non-default Account & Data Files Outlook VBA and Custom Forms 3
P Limited Support for 3rd Party Mail in new Outlook? Using Outlook 1
O Any 3rd party tool that sync (mirror) from Outlook Calendar to Google Calendar? Using Outlook 5
T Outlook is categorizing emails incorrectly Using Outlook 1
R Legacy Outlook on Mac Email Cache Using Outlook 0
A Outlook can't remember, Exchange password. Using Outlook 6
S Related messages show in main Outlook window vice new Advanced Find windows Using Outlook 1
H Force Outlook 2019 with GMail 2-Step to Require Login? Using Outlook 0
G Retaining Tabs in outlook body Using Outlook 2
V Setting up Outlook 2021 on new computer Using Outlook 2
G Add Map It button to Custom Contacts Form in Outlook Outlook VBA and Custom Forms 1
X Custom icon (not from Office 365) for a macro in Outlook Outlook VBA and Custom Forms 1
Victor_50 Problem - Google Workspace will stop "unsafe" access to Outlook end 2024 Using Outlook 3
C New pc, new outlook, is it possible to import auto-complete emailaddress Using Outlook 4
T Outlook 365 won't take new working password Using Outlook 0
S Create Outlook Task from Template and append Body with Email Body Outlook VBA and Custom Forms 4
P Can't add custom field to custom Outlook form, it always adds to the Folder instead Outlook VBA and Custom Forms 2
B Sync Outlook Public Folders to Contacts Using Outlook 2
D Delete Outlook emails from MS server Using Outlook 12
B Outlook tasks and PDF Using Outlook 4
D Outlook 2019 is no longer asking for password ... Using Outlook 5
Kika Melo How to mark as Junk any message not from Contacts (in Using Outlook 3
L Outlook attachments from OneDrive as links Using Outlook 0
G Outlook 365 My iCloud Outlook doesn’t work after reinstalling Microsoft365 on Windows 10 PC – now I get error message on contacts and calendar Using Outlook 1
T How to Export & Import GMAIL Contacts into Outlook 2021 ? Using Outlook 4
M Synchronization and backup of Outlook from local to server. Using Outlook 12
T How to get an EVENT COLOR option in Outlook 2021 ? Using Outlook 0
K How can I delete an e-mail from Outlook Using Outlook 1
V Outlook Error The Attempted operation Failed. An Object Could Not be found Outlook VBA and Custom Forms 0
P Yahoo/IMAP folder rename by Outlook desktop 365 Using Outlook 0
A Outlook 2019 folder counter Using Outlook 0
A Relocate Search Bar in Outlook Using Outlook 2
e_a_g_l_e_p_i Need clarification on 2-Step Verification for Gmail using Outlook 2021 Using Outlook 10
L Opening People Outlook 2021 Using Outlook 2
e_a_g_l_e_p_i Outlook 2021 not letting me setup my Gmail using pop Using Outlook 1
Geldner Problem submitting SPAM using Outlook VBA Form Outlook VBA and Custom Forms 2
P VBA to add email address to Outlook 365 rule Outlook VBA and Custom Forms 0
M Outlook 2016 outlook vba to look into shared mailbox Outlook VBA and Custom Forms 0
P Can no longer sync Outlook with iPhone calendar after iPhone update to 17.1.1 Using Outlook 7
O Outlook - Switch from Exchange to IMAP Using Outlook 2
e_a_g_l_e_p_i Is it possible to have a reminder in Outlook 2021 for every 90 days Using Outlook 3
farrissf Outlook 2016 Optimizing Email Searches in Outlook 2016: Seeking Insights on Quick Search vs Advanced Search Features Using Outlook 0

Similar threads