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Outlook not able to send emails with attachments greater than 3MB

Hi.
I hope someone can help with a very strange issue. My client uses a shared hosted exchange (running Exchange 2010) platform for their emails. This has been running fine until yesterday.
If a user send an email with attachments greater than 3mb they just sit in the outbox trying to send and hold everything else up.
We contacted out internet service provider to check the firewall and MPLS setup to see if anything was limiting sending emails but no thing has found to be causing that. The issue is also experienced via other internet connections so it is not specific to the company network.
The company that hosts the Exchange platform say the cannot find any issues on their side and if there was it would be affecting all the other clients on the share platform.
The were also not able to replicate the issue on their side.

We are running MS Office home & business 2010, 2013 & 2016 which are all experiencing this issue.

Does anyone have any other troubleshooting suggestions in order to find this root cause?
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bax2000
Asked:
bax2000
2 Solutions
 
AndyIt ConsultantCommented:
This does sound like a size limit either in the firewall or exchange settings.
I would ask the exchange hosting company to specifically check the exchange organisation - global settings - transport settings for maximum send size
Also check the exchange organisation - Send connectors - open any send connectors - general tab for Maximum message size.
Also, check some of your users Mailbox settings in Mail Flow Settings - Sending message size.

Also, check the users mailbox limit to make sure he's not over a sending limit.

Finally, you can edit the Web.config file on a Client Access server to enable large messages to be sent by using Outlook Web App. Outlook Web App is an application that uses ASP.NET and is affected by the configuration of ASP.NET settings.
The ASP.NET setting that determines the maximum amount of data that the Web browser can submit to the Client Access server is maxRequestLength. The maxRequestLength setting is found in the Web.config file. If the setting for the maximum message size for sending on a mailbox is more than the maxRequestLength setting, messages that are sent from Outlook Web App that exceed the maxRequestLength value will generate an error that might be confusing to users. To avoid this, you must configure the maxRequestLength to be at least as large as the largest maximum send size on the mailboxes in your organization.

Regarding their comment:
The company that hosts the Exchange platform say the cannot find any issues on their side and if there was it would be affecting all the other clients on the share platform.
This would not be true if your users had the message size restrictions set.

If it's not the hosting company then it sounds more likely to be a firewall setting or if you have mimecast or other scanning services this could be restricting the size.
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bax2000Author Commented:
@Andy
Thanks for the reply. We have already check the firewall and there is no limitation for email sending.
Sending large attachments via OWA also work fine. We only experience this issue when sending via MS Outlook.
Could it be an office version issue? My client used MS Office Home and Business and I tried it on my personal computer that have MS Office Professional Plus and that worked find. I even had this connected to the company network.
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AndyIt ConsultantCommented:
Strange, Outlook 2010 at least should be fine up to 20MB

If the clients are in cached mode, try without cached mode on.

Also, guessing OWA is on the web (external) and outlook is local which means it's a local network issue, which other internet connections have you tried on?
Check the reg sizes are set OK or not set:
Open the registry editor and browse to:

Outlook 2016:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences

Outlook 2013:
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Preferences

Outlook 2010:
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences

Then add a new DWORD value: MaximumAttachmentSize
Unlimited message size uses a value of 0. For a specific message size (recommended) enter the decimal value in Kb. You may want to round the value down to allow for overhead, so 50MB = 50000.
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bax2000Author Commented:
- Yes OWA is external and works fine.
- Outlook with Cache off also does not send with the larger attachment, it just hangs.
- The users on the exchange server have limits of 30MB attachments so size should not be an issue.
- If we send via Android or iOS mail client we also have no issues. The issue seems to point to Outlook. Very strange!!
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AndyIt ConsultantCommented:
I agree, did you check/add the reg entries?
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BillBondoCommented:
Shot in the dark but we had symantec mail security device that knocked down our attachment sizes after it did an update.
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AndyIt ConsultantCommented:
Good point, also has happened before on other AV products such as Norton.
Also check your outlook send/receive groups / schedules.
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suriyaehnopCommented:
Does the issue happened only on single user or all of your users. If it is the first one, could you check the mailbox quota? Does it exceeded?
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bax2000Author Commented:
We use ESET Nod32. There was a new update that must have cause this issue. Once I turned off HTTPS Checking on the computers the emails were sending fine again.
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