Why are only some email attachments being lost to G Suite accounts?

Attachments can be lost due to several reasons, including incorrect Java API implementation (e.g., wrong MIME types), stringent recipient-side G Suite security policies, or even the content within the attachment being flagged as suspicious. Sometimes, intermediate mail gateways can also interfere. This is why it's important to look at email deliverability issues from all angles.

How do G Suite's security policies affect attachment delivery?

G Suite (and Gmail ) employs advanced spam and malware filters. While it doesn't typically strip legitimate attachments, administrators can configure content compliance rules or integrate third-party security solutions that may remove attachments deemed risky. Poor sender reputation can also trigger stricter filtering.

Can certain file types like PDFs or XMLs cause attachment issues?

Yes, while PDFs and XMLs are generally safe, their internal structure or embedded elements can sometimes trigger security flags if they mimic malicious content. Ensuring proper encoding and clean content is vital. If your emails are rejected by Gmail , it's often linked to content.

What role do SPF, DKIM, and DMARC play in attachment delivery?

Proper email authentication via SPF, DKIM, and DMARC is crucial. These records help G Suite verify the authenticity of your emails. If DMARC verification fails , emails may be treated as suspicious, leading to attachments being stripped or the email being rejected entirely. Regularly reviewing your email deliverability test reports can help identify such issues.

Why are email attachments being lost when sending from Java API to G Suite accounts? - Troubleshooting - Email deliverability - Knowledge base

Dealing with email attachments that mysteriously disappear can be incredibly frustrating, especially when they contain critical information like invoices or important documents. When these issues occur with emails sent from a Java API and intended for

G Suite accounts, it points to a specific set of challenges. This isn't a random occurrence, but rather a symptom of underlying configuration, policy, or even content-related issues.

Many email systems, including those powering Gmail and G Suite, have robust security measures in place. These measures are designed to protect users from malicious content, but they can sometimes inadvertently filter out legitimate attachments if certain criteria are not met. The problem becomes more complex when specific file types, such as PDFs or XML files, are consistently affected, while others, like plain text, are delivered without issue.

My goal is to help you navigate these complexities. We will explore the common reasons why attachments might be lost, from API-level implementation details to G Suite's internal filtering mechanisms, and provide practical steps to diagnose and resolve these frustrating delivery problems.

Troubleshooting initial steps

Before diving into complex solutions, it's crucial to confirm the basics. The first step is always to verify that the attachments are actually being sent correctly from your Java application. This involves checking the outgoing mail server logs and, if possible, reviewing the raw email content before it leaves your system.

One common pitfall is the incorrect handling of MIME types or character encodings within the Java Mail API. Ensure that your code explicitly sets the correct Content-Type and Content-Disposition headers for each attachment. A mismatch or omission can lead to the recipient's mail client failing to render or recognize the attachment, even if the bytes are technically present in the email.

Also, consider the size of your attachments. While your 10-35KB PDF and XML files are generally small, some mail servers, or even specific user configurations, might have unexpected limits. Although it's less common for G Suite, external mail transfer agents (MTAs) that process mail before it reaches the final G Suite inbox could be configured with stricter size restrictions.

Understanding G Suite's attachment handling

G Suite's email infrastructure is highly sophisticated, designed to manage large volumes of mail and filter out unwanted content like spam and malware. It typically does not strip legitimate attachments unless there are specific policies in place that trigger such actions. This means if attachments are being lost, it’s likely due to a perceived security risk or a misconfiguration on either the sending or receiving end.

Administrators of G Suite accounts have the ability to set up content compliance rules, attachment compliance rules, and even integrate third-party security solutions that scan and potentially remove attachments. If you are sending to multiple G Suite domains and only some are experiencing issues, it strongly suggests a recipient-side policy. Checking the G Suite Admin Console for recipient domains, if possible, is an important step. Often, if an attachment is blocked due to a policy, the recipient might receive a notification.

The type of attachment also matters. While PDFs and XMLs are common business formats, their content can sometimes trigger security flags if they contain executable scripts, embedded objects, or unusual formatting that mimics malicious content. This is where sender reputation and email authentication also play a role, influencing how strictly G Suite applies its filtering rules. Problems can arise even when regular emails are going to spam.

Common Java API implementation issues

When using Java API to send emails, the way attachments are constructed and added to the message is critical. Incorrect handling can lead to corrupted attachments or attachments that are simply not recognized by the receiving mail server, causing them to appear 'lost'.

A common mistake involves how MimeBodyPart and MimeMultipart objects are used. Each attachment should be a separate MimeBodyPart, correctly setting its data source and file name. The entire message, including the body and all attachments, should then be encapsulated within a MimeMultipart with the appropriate mixed subtype. This ensures the email is correctly formatted for recipients, regardless of their mail client.

Example of Java Mail API sending with attachmentjava

import java.io.File;
import java.io.IOException;
import java.util.Properties;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.FileDataSource;
import javax.mail.BodyPart;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;

public class EmailSender {

    public static void sendEmailWithAttachment(String to, String from, String host, String username, String password, String subject, String body, String attachmentPath) {

        Properties props = new Properties();
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.starttls.enable", "true");
        props.put("mail.smtp.host", host);
        props.put("mail.smtp.port", "587");

        Session session = Session.getInstance(props, new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

        try {
            MimeMessage message = new MimeMessage(session);
            message.setFrom(new InternetAddress(from));
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
            message.setSubject(subject);

            BodyPart messageBodyPart = new MimeBodyPart();
            messageBodyPart.setText(body);

            MimeMultipart multipart = new MimeMultipart();
            multipart.addBodyPart(messageBodyPart);

            if (attachmentPath != null && !attachmentPath.isEmpty()) {
                MimeBodyPart attachmentPart = new MimeBodyPart();
                DataSource source = new FileDataSource(attachmentPath);
                attachmentPart.setDataHandler(new DataHandler(source));
                attachmentPart.setFileName(new File(attachmentPath).getName());
                multipart.addBodyPart(attachmentPart);
            }

            message.setContent(multipart);

            Transport.send(message);

            System.out.println("Email sent successfully with attachment!");

        } catch (MessagingException | IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        // Example Usage:
        // sendEmailWithAttachment("recipient@example.com", "sender@yourdomain.com", "smtp.yourmailprovider.com", "yourusername", "yourpassword", "Invoice", "Please find attached your invoice.", "/path/to/your/invoice.pdf");
    }
}

Verify that your Java API setup is robust enough to handle various file types and sizes. Issues with attachment encoding, particularly for binary files like PDFs, or how the email content is structured as a multipart message, can cause these files to be misinterpreted or stripped by G Suite's servers. Ensuring proper error handling and logging within your application can also help pinpoint exactly where the attachment might be failing, which is key to improving email deliverability.

Advanced security and filtering considerations

Beyond the basic technical implementation, a significant factor in email delivery is sender reputation and adherence to email authentication standards. While G Suite itself might not be stripping attachments, poor sender reputation can lead to your emails being subjected to more stringent filtering, increasing the likelihood of attachments being flagged or removed.

Ensure your sending domain has properly configured SPF, DKIM, and DMARC records. These protocols help G Suite verify that the emails are legitimately coming from your domain, reducing suspicion. A misconfigured DMARC policy, for example, could lead to emails failing authentication, resulting in rejection or spam placement, and potentially the stripping of attachments as a protective measure. It's also vital to consider if your sending IP is on any email blacklist (or blocklist), as this can severely impact delivery. Understanding how email blacklists actually work is crucial for proactive monitoring.

Some G Suite environments might route incoming mail through a third-party email security gateway (e.g.,

Microsoft 365 Exchange or other solutions) before it reaches the final inbox. These external services often have their own set of content filtering rules and may be more aggressive in stripping attachments they deem suspicious or malformed. While rare, it's worth investigating if the recipient's G Suite setup involves such an intermediate step, as these services would apply their own policies independent of

Google's native filtering.

Finally, the content within the PDF or XML itself could be triggering filters. For instance, if the XML file contains certain tags or structures commonly associated with phishing or malware, or if the PDF has embedded elements that are flagged as risky, they might be removed. Even a small file size won't prevent filtering if the content itself is deemed suspicious. Reviewing the content of these specific attachments for anything that could be misinterpreted as malicious is a crucial diagnostic step.

Views from the trenches

Best practices

Validate your Java Mail API implementation to ensure correct MIME type and encoding settings for attachments.

Regularly monitor your email sending logs to confirm attachments are leaving your server as expected.

Ensure your domain has robust SPF, DKIM, and DMARC authentication records configured properly.

Common pitfalls

Assuming small attachment sizes will bypass all security filters; content is often more critical than size.

Failing to confirm the actual outgoing email structure, leading to misdiagnosis of delivery issues.

Not considering recipient-side email security gateways or specific G Suite admin rules that strip attachments.

Expert tips

Implement robust logging in your Java application to capture details about attachment processing and sending outcomes.

Consider sending test emails with simplified versions of your problematic attachments to isolate potential content-based triggers.

Utilize Google Postmaster Tools for your sending domain to monitor reputation metrics, spam rates, and delivery errors.

Marketer view

Marketer from Email Geeks says that G Suite business domains might be losing attachments due to specific antivirus, third-party services, or inbox settings, especially for invoices with small PDF and XML attachments.

2020-02-05 - Email Geeks

Expert view

Expert from Email Geeks says that G Suite typically does not strip attachments and that inbox settings could be a factor. If other domains are running their own filtering, they might strip attachments if they appear suspicious.

2020-02-05 - Email Geeks

Resolving attachment delivery failures

The issue of email attachments being lost when sending from a Java API to G Suite accounts often stems from a combination of factors, ranging from incorrect API implementation to sophisticated recipient-side filtering. It’s rarely a single, obvious problem.

By systematically checking your Java Mail API configuration, ensuring proper MIME type handling, verifying attachment content for suspicious elements, and confirming your sender authentication (SPF, DKIM, DMARC), you can significantly improve the reliability of your email attachments. Engaging with the recipient's IT team, if possible, can also provide valuable insights into specific G Suite policies that might be impacting delivery.