How to attach multiple files when sending emails through Mailgun API in Java

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1

I need help with sending emails that have more than one file attached using Mailgun’s API in Java. Right now I can only get one file to work but I want to include several attachments in the same email.

Here’s my current code that works for a single attachment:

public static JsonNode sendEmailWithAttachments() throws UnirestException {
    HttpResponse<JsonNode> response = Unirest.post("https://api.mailgun.net/v3/" + DOMAIN_NAME + "/messages")
            .basicAuth("api", SECRET_KEY)
            .queryString("from", "Admin <[email protected]>")
            .queryString("to", "[email protected]")
            .queryString("subject", "Your Documents")
            .queryString("text", "Please find your documents attached")
            .queryString("html", "<p>Your requested files are attached below</p>")
            .field("attachment", new File("/documents/report.pdf"))
            .asJson();

    return response.getBody();
}

This works fine for one file but I can’t figure out how to add more files to the same email. I tried calling the field method multiple times but that doesn’t seem to work properly. What’s the correct way to handle multiple file attachments with Mailgun?

Thanks for any suggestions.

2

Yeah, this is a super common issue with Mailgun’s API. You’re doing it right by calling field multiple times - just need to tweak the approach. Chain multiple field calls for each attachment, but use the same “attachment” parameter name for all of them:

public static JsonNode sendEmailWithAttachments() throws UnirestException {
    HttpResponse<JsonNode> response = Unirest.post("https://api.mailgun.net/v3/" + DOMAIN_NAME + "/messages")
            .basicAuth("api", SECRET_KEY)
            .queryString("from", "Admin <[email protected]>")
            .queryString("to", "[email protected]")
            .queryString("subject", "Your Documents")
            .queryString("text", "Please find your documents attached")
            .queryString("html", "<p>Your requested files are attached below</p>")
            .field("attachment", new File("/documents/report.pdf"))
            .field("attachment", new File("/documents/invoice.pdf"))
            .field("attachment", new File("/documents/summary.docx"))
            .asJson();

    return response.getBody();
}

I’ve used this in production and it works perfectly. Mailgun wants multiple fields with the same name, not different parameter names for each file.

3

Hit this exact problem last year building a document delivery system. Took me way too long to figure out that order matters with Unirest.

What fixed it for me: build the request step by step, then add attachments after you’ve got the basic email stuff set up. Here’s what works:

public static JsonNode sendEmailWithAttachments() throws UnirestException {
    HttpRequest request = Unirest.post("https://api.mailgun.net/v3/" + DOMAIN_NAME + "/messages")
            .basicAuth("api", SECRET_KEY)
            .queryString("from", "Admin <[email protected]>")
            .queryString("to", "[email protected]")
            .queryString("subject", "Your Documents")
            .queryString("text", "Please find your documents attached")
            .queryString("html", "<p>Your requested files are attached below</p>");
    
    // Add all attachments
    request.field("attachment", new File("/documents/report.pdf"))
           .field("attachment", new File("/documents/contract.pdf"))
           .field("attachment", new File("/documents/terms.pdf"));
    
    return request.asJson().getBody();
}

This handles 2-15 attachments per email no problem.

4

just loop through ur files and call field() for each one. works every time for me. something like this:

File[] files = {new File("/docs/file1.pdf"), new File("/docs/file2.docx")};
for(File f : files) {
    request.field("attachment", f);
}

dont exceed Mailgun’s 25MB limit though or it’ll fail silently.