MailKit | A cross-platform NET library for IMAP, POP3, and SMTP | Email library

Before I explain how to save the message in your Sent IMAP folder, I first want to bring attention to a few things.

1. smtp.Timeout = 10000; It's probably best to not override the default timeout (which I believe is 120,000. 10000 is 10 seconds).
2. You currently have a mix of sync and async calls to the SmtpClient. You should pick sync or async and stick with it (at least if it's all within the same method).

Okay, now on to your question.

Since you are using WASM (aka Blazor WebAssembly), you will probably be not able to use an SMTP client client-side.

To quote an answer to a similar issue on GitHub:

It is unlikely than an SMTP client is going to work in Blazor WebAssembly. Ultimately Blazor is subject to the same restrictions that any other application running in the browser.

That means you can't create TCP or UDP connections since browsers don't allow that.

You'll likely need to do this from an endpoint on a server through a Rest API.

This is what I would actually do, too:

1. Create a server-side ASP.NET Core Web API endpoint.
2. Protect the API endpoint with some API key to not expose it publicly.
3. Pass the related data from your WASM to that Web API.
4. Send the actual email message via MailKit from that server-side API.

First, I need to make sure that I correctly understand what you mean when you say that you are trying to get your "replies on an email".

What I assume you mean right now is that someone sent you a message (let's call him Joe) and you replied back to him and you want to write a program that will connect to the IMAP server and download your reply back to Joe.

Let's pretend that the Subject of the message is "drinks?"

In other words:

You have 2 options:

1. Increase the timeout using the ImapClient.Timeout property. (That said, 1 minute is less than the default timeout which is 2 minutes)
2. As Max points out in the comments below, properly handle exceptions and retry (which often will require reconnecting the ImapClient).

Include this namespace

You can't use or inside the function call like that; you need two separate Contains() calls. Also, this can be way shorter:

Please try to use string[] eMailTo, it should be useful to you.

The POP3 protocol is very basic and does not support any way of searching. The IMAP protocol would be a better protocol for what you want to do, but if you don't have that option, you could (potentially) improve network performance of your app by downloading only the headers in order to do your filtering and then, if it matches, download the full message.

For example:

You need to properly quote the name if it contains @ symbols or ..

Those are special characters that are required to be quoted by the email specifications.

In other words, the correct string would be: