IOException while sending message - possible file size problem


I believe I am receiving an error related to email attachment file size but the actual message is not descriptive enough for me to be sure.

When attempting to attach files to an email that are of ~3mb each, emails seem to be properly sent, but when I attempt to attach a 25mb 10 second video file, the emails fail to send and I receive errors like the one identified below.

Could someone help me to determine whether this is an issue that’s directly caused by file size? Or if maybe it has to do with the maximum CloudCode execution time? Or some other problem altogether?

Thank you

Backendless Version (3.x / 5.x, Online / Managed / Pro )

Online Cloud 99 trial - not sure if 3.x or 5.x

Client SDK (REST / Android / Objective-C / Swift / JS )

Java CloudCode

Application ID


Expected Behavior

Please describe the expected behavior of the issue, starting from the first action.

  1. Use Backendless.Messaging.sendEmail() to send an email with attachments.
  2. Email recipient successfully receives email.

Actual Behavior

Please provide a description of what actually happens, working from the same starting point.

  1. Use Backendless.Messaging.sendEmail() to send an email with attachments.
  2. Email recipient receives nothing.
  3. I receive an email telling me that “Error occurred during email sending”

2022-12-24 08:22:07,564 | SMTP Logger | DEBUG | Going to send email with subject ‘subject_omitted’ for recipients [recipient_omitted].
2022-12-24 08:22:11,736 | SMTP Logger | ERROR | Error occurred during email sending. Subject ‘subject_omitted’. Recipients [recipient_omitted]. : IOException while sending message

Reproducible Test Case

  1. Add a file to the Backendless file store of ~25mb and attempt to attach it to an email with the Java CloudCode SDK.

Hi, @Mark_Moline

We do not set any limits on the size of the attachments in the files on our side. I was able to reproduce the problem in your application. The problem seems to be related to a file size limitation on the SMTP side.
The error I got when testing sending emails with attachments from your application:

550 Read data error, maximum message size exceeded.

About the IOException error, in some cases I was getting it instead of human-readable, even though the attached file was the same. We didn’t find anything regarfing that on our server, the error is coming from the SMTP server in that way.



Thank you very much for looking into this!