Cast Amazon SES emails, stored in S3 buckets, to MimeMessage type (MimeKit)

Question

I need to read incoming email messages, with the following constraints:

1. An Amazon SES rule stores the incoming emails to a S3 bucket;
2. These emails then need to be cast to the MimeMessage type, of the MimeKit C# library, in order to work well with legacy code.

Thing is when I try to convert the emails to the MimeMessage, I get the exception "The filename, directory name or volume label syntax is incorrect."

How can I make the conversion to MimeMessage work? Should I parse the contents of the email messages with Regex for it?

I know I could integrate Amazon SES with Amazon WorkMail to receive my messages in the Mime format, which would make it easier for me. But I would avoid having to subscribe to another paid service from Amazon if I could.

I post below both my code and the message error, to better illustrate the problem:

    public GetMailController(AmazonS3Client s3Client, IConfiguration configuration)
    {
        _s3Client = s3Client;
        _config = configuration;
    }

    [HttpGet(Name = "Get")]
    public IEnumerable<MimeMessage> Get()
    {
        string AwsS3Bucket = _config.GetValue<string>("AwsS3Bucket");
        List<MimeMessage> mails = new();
        List<string> bucketKeys = GetBucketIds();
        foreach (string k in bucketKeys)
        {
            GetObjectResponse response = _s3Client.GetObjectAsync(new GetObjectRequest() { BucketName = AwsS3Bucket, Key = k }).GetAwaiter().GetResult();
            using (Stream responseStream = response.ResponseStream)
            using (StreamReader reader = new StreamReader(responseStream))
            {
                string content = reader.ReadToEnd();
                try
                {
                
                    var mail = MimeMessage.LoadAsync(content).GetAwaiter().GetResult(); // Exception: "The filename, directory name or volume label syntax is incorrect."
                    mails.Add(mail);
                }
                catch (Exception exc)
                {
                    return null;

                }
            }
        }
        return mails;
    }

Resulting error message

The filename, directory name or volume label syntax is incorrect. 

I tried using the MimeKit method MimeMessage.Load() to parse a email message in MIME format, but insted got an exception: The filename, directory name or volume label syntax is incorrect.

Answer 1

The MimeMessage.Load() method expects to receive either a filename (file path) or a stream as an argument.

Since you're providing it with the string-equivalent of the stream, it thinks you're providing it a file name - hence the filename, directory name or volume label syntax is incorrect error.

Directly use the stream you get from the GetObjectResponse, like so:

GetObjectResponse response = _s3Client.GetObjectAsync(new GetObjectRequest() { BucketName = AwsS3Bucket, Key = k }).GetAwaiter().GetResult();
using (Stream responseStream = response.ResponseStream)
{
    try
    {
        var mail = MimeMessage.Load(responseStream);
        mails.Add(mail);
    }
    catch (Exception exc)
    {
        return null;
    }
}

---

_{I would also recommend to use await instead of .GetAwaiter().GetResult().}