[Python] Unable to send emails with attachments of size greater than ~300KB via SES

I'm using the code below to send emails with attachments. There can be scenarios to send emails with multiple attachments (usually PDF files). Each file size will not exceed 2MB. The following code is only working if the file size is less than ~300KB. If the file size is smaller than ~300KB, email sent with attachment. if file size is larger an empty document sent with the name "no name" in the attachment.

Is there any limitation in sending files greater than 300KB via SES.

msg = MIMEMultipart("mixed")
msg["Subject"] = subject
msg["From"] = sender
msg["To"] = ", ".join(recipients)

for attachment in attachments:
       if os.path.exists(attachment):
           attachment_obj = MIMEApplication(open(attachment, "rb").read())
           attachment_obj.add_header(
                 "Content-Disposition",
                 "attachment",
                 filename=os.path.basename(attachment),
           )
           msg.attach(attachment_obj)
        
msg_body = MIMEMultipart("alternative")
email_body = MIMEText(body.encode(charset), "plain", charset)
msg_body.attach(email_body)
msg.attach(msg_body)

response = ses_client.send_raw_email(
                Source=sender,
                Destinations=recipients,
                RawMessage={
                    "Data": msg.as_string(),
                },
            )

Observed similar behaviour in Java also. but AWS docs suggests the maximum supported size is 10MB. What could be the reason for this?