0 votes

We have the configuration:
- 2017 licenced version of Mail.dll
- Exchange-Mailserver (stable 2019) in the local network of the Mail-Client
- Exchange with default-Settings acts as "Mail-Relay" on port 25 (no auth)
- Normal SMTP.Connect(SERVER,PORT); // no ConnectSSL
- Normal builder.Create() - MimeEncoding for TextData only
- Body with Text only under 1kByte - No Attachgments
- Only one valid address in TO and FROM, no CC, BCC and ReplyTO
- SendMessageStatus is Success after 5,1 seconds
- Productive Outlook or Outlook-Web-Access takes under 100ms
- On other external Mail-Servers with Auth/TLS 1.2 this is "fast engouth" (0,4 sec).
- Still no wireshark analyse is possible due to our enterprice IT...

For no Auth/SMTP-Relay:
Do you have an idea why this could be so slow or is there a parameter that we missed? Is there a bug or is the performance in new version of Mail.dll essential better?


Thanks for the answer. We create all mail parameters. The only parameter that is set after the connect and before the SendMessage() is the

IMail imail = MailBuilder.Create(); 


    = MimeEncoding.QuotedPrintable;

To make these step bevore the connect has no effect.

Is it possible get a deeper log-level or is it possible to find out which limilabs- or mailserver-component is so slow?

Here is my complete log:

13:10:18 S: 250-EXCH-PERMTEST.XXXXXXXXXXX.de Hello [X.X.X.117]
13:10:18 S: 250-SIZE 37748736
13:10:18 S: 250-PIPELINING
13:10:18 S: 250-DSN
13:10:18 S: 250-STARTTLS
13:10:18 S: 250-X-ANONYMOUSTLS
13:10:18 S: 250-AUTH NTLM
13:10:18 S: 250-X-EXPS GSSAPI NTLM
13:10:18 S: 250-8BITMIME
13:10:18 S: 250-BINARYMIME
13:10:18 S: 250-CHUNKING
13:10:18 S: 250-SMTPUTF8
13:10:18 S: 250 XRDST
13:10:25 C: RCPT TO:user01@XXXXXXXXxXXXXXXX.de
13:10:25 C: NOOP
13:10:25 S: 250 2.1.0 Sender OK
13:10:26 S: 250 2.1.5 Recipient OK
13:10:30 S: 250 2.0.0 OK
13:10:31 C: BDAT 591 LAST
13:10:31 C (591 bytes): Content-Type: text/plain;
 Content-Transfer-Encoding: 7bit
 MIME-Version: 1.0
 Date: Thu, 07 Nov 2019 13:10:25 +0100
 Message-ID: 0169c2e9-7e72-4a9b-b469-a968a7fb511e@mail.dll
 Subject: =?utf-8?Q?Genehmigungsaufgabef=C3=BCrEingangsrechnungbis31=2E12?=
 From: muster.moebelmeister@XXXX.de
 To: user01@YYYY.de

 Liebe Kollegin, lieber Kollege,

13:10:31 S: 250 2.6.0 0169c2e9-7e72-4a9b-b469-a968a7fb511e@mail.dll [InternalId=1417339207682, Hostname=EXCH-PERMTEST.XXXXXXXXXXXXXX.de] 2057 bytes in 0.097, 20,499 KB/sec Queued mail for delivery
13:10:31 C: QUIT
by (400 points)
edited by
Question was edited to include the log, same as the answer.

1 Answer

0 votes

Make sure that email creation happens before you even try to connect.

This way you can measure what takes most time: email creation, connecting or sending.

Consider turning on logging:

5.1 sec is very long, I'm pretty sure the problem is not with Mail.dll.
Maybe your server is throttling you?

Create message before connecting otherwise log times make no sense.

There is almost 7 seconds gap after connection is established and first MAIL FROM is send:

13:10:18 S: 250 XRDST

Why is that? - I assume this is were you create a message and it is slow for some reason.

Then the server responses start to be extremely slow:

13:10:25 C: NOOP
13:10:25 S: 250 2.1.0 Sender OK
13:10:26 S: 250 2.1.5 Recipient OK
13:10:30 S: 250 2.0.0 OK

This usually means that the server is throttling you.

Please consult you server administrator: maybe authenticated accounts are not being throttled.

by (298k points)
edited by