Publish emails with attachments having size greater than 256kb

We have .net 6 application from where we are publishing email/text notification using masstransit and subscribing in another application from same solution. Publishing email with attachment is working fine if file size is less than 256kb though it's failing to publish email if attachment size exceeds 256kb size limit. The question here is how can i publish such emails with attachments exactly?

Please find the exception i am getting while publishing email with big size attachement *Amazon.SimpleNotificationService.Model.InvalidParameterException: Invalid parameter: Message too long ---> Amazon.Runtime.Internal.HttpErrorResponseException: Exception of type 'Amazon.Runtime.Internal.HttpErrorResponseException' was thrown. at Amazon.Runtime.HttpWebRequestMessage.GetResponseAsync(CancellationToken cancellationToken) *