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In Gmail, attachments cannot exceed 25 MB, which means Cognos Analytics cannot successfully deliver a report attachment (Excel, PDF)  via email that exceeds 25 MB.

Example Attachment Error Messages

When Cognos Analytics cannot deliver the attachment due to a size limitation, recipients will receive a notification via email like one below.

In this example in v11.0.8, the user set the report to run in the background and deliver the report by email and save. The user was able to retrieve the saved PDF output in Cognos Analytics.

Subject line
 A new version of Codes and Descriptions is available

Attachment message
CNC-SDS-0423 The attachment 'Codes and Descriptions.pdf', in 'application/pdf' format, of size 181.12MB was missing from the request. It was probably removed due to exceeding a maximum size setting on the sending service.

In this example in v10.2.2, the schedule was set to email the report as the only delivery method.

Subject line
 Send failed: Report: Codes and Descriptions

Body
 We were unable to send a message to one or more recipients. Please contact your administrator.
 Subject: Send failed: Report: Codes and Descriptions
 Date: Tue, Mar 17, 2015 11:57:12 EDT
 Error Message: CNC-SDS-0335 Error returned from SMTP Server. The error message was: [552 5.3.4 Error: message file too big]. The message could not be sent.

Size Limits

Ultimately, anything bigger than 25 MB will not be delivered by Gmail. However, there are multiple limits at play when a Cognos Analytics email attachment cannot be sent because it is too big.

• Gmail limit: 25 MB
• Cognos mail attachment limit: 30 MB
• Mail relay limit: 35 MB
• Batch Report Limit: 30 MB

How Congnos Analytics Determines the Attachment Size

Messages expand and then shrink during sending, so when a message fails due to a size limitation, the size listed in the Cognos Analytics failure message may be inflated.

From IBM PM58043: 

MAIL ATTACHMENT LIMIT SETTING DOES NOT TAKE COMPRESSED ATTACHMENT SIZE INTO ACCOUNT
When configuring the 'Maximum size of an email message for  delivery service in MB', the size of the attachments is examined  only before compression, resulting in an inability to send  attachments that would typically be acceptable when compressed.

Note for Administrators

On 2/12/19, the "Maximum size of an uncompressed email attachment for batch report service in MB" was changed from 20 to 30.