阻止 Exchange 2013 将邮件 body text/plain 转换为 HTML
Prevent Exchange 2013 from converting message body text/plain to HTML
在使用 IMAP 连接到 Microsoft Exchange 2013 帐户时，我正在使用 MailKit v2.8 解析电子邮件中的数据。发送到我的 Exchange 收件箱的 body 封邮件在 100% 的时间里都是“text/plain”。此过程对于新电子邮件完全正常（并且已经投入生产使用了几个月），但是这些电子邮件的 replies/forwards 可能在提取时由 Exchange 转换为 HTML。服务器上回复邮件的 header 仍然指定消息 body 是“text/plain”。 Outlook 也以纯文本显示响应，但出于某种原因，当我尝试使用 MailKit 获取消息摘要的 TextPart 时，它返回 null。
MailKit 邮件获取代码：
using var imap = new ImapClient {
ServerCertificateValidationCallback = (mySender, cert, chain, sslPolicyErrors) => { return true; },
CheckCertificateRevocation = false
};
try {
await imap.ConnectAsync(_config.ImapServer, _config.ImapPort, SecureSocketOptions.SslOnConnect);
imap.AuthenticationMechanisms.Remove("XOAUTH2");
await imap.AuthenticateAsync(_config.ImapUsername, _config.ImapPassword);
var inbox = imap.Inbox;
if (!string.IsNullOrWhiteSpace(_config.Inbox)) { // set inbox to subfolder for devenv
inbox = await imap.Inbox.GetSubfolderAsync(_config.Inbox);
}
await inbox.OpenAsync(FolderAccess.ReadWrite);
var uIds = await inbox.SearchAsync(SearchQuery.All);
var msgs = await inbox.FetchAsync(uIds, MessageSummaryItems.UniqueId | MessageSummaryItems.BodyStructure | MessageSummaryItems.Envelope);
foreach (var msg in msgs) {
var bodyPart = msg.TextBody; // <-- this returns null for the latter email, but contains a body for the former
var body = await inbox.GetBodyPartAsync(msg.UniqueId, bodyPart) as TextPart;
if (_config.SendingAddresses.Any(msg.Envelope.From.Mailboxes.Select(a => a.Address).Contains)) { // sent from valid address
// parse and process email body
} else {
// discard and expunge
}
}
} catch (Exception e) {
// log exception
}
为简洁起见，这里有一个例子。使用 MailKit 获取时，此电子邮件包含文本Body：
Received: from [ExchangeHost] ([ExchangeIP]) by [ExchangeHost]
([ExchangeIP]) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Thu, 6 Aug 2020
17:30:12 -0400
Received: from [SenderHost] ([SenderIP]) by
[ExchangeHost] ([ExchangeIP]) with Microsoft SMTP Server id 15.0.1320.4
via Frontend Transport; Thu, 6 Aug 2020 17:30:11 -0400
IronPort-SDR: [redacted]
X-IronPort-AV: [redacted]
X-AuditID: [redacted]
MIME-Version: 1.0
Message-ID: <[redacted]>
From: <[SenderAddr1]>
To: <[MyExchangeAddr]>
Date: Thu, 6 Aug 2020 14:30:03 -0700
Subject: [redacted]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
Return-Path: [SenderAddr1]
X-MS-Exchange-Organization-AuthSource: [ExchangeHost]
X-MS-Exchange-Organization-AuthAs: Anonymous
X-GFI-SMTP-Submission: 1
X-GFI-SMTP-HelloDomain: [SenderHost]
X-GFI-SMTP-RemoteIP: [SenderIP]
X-MS-Exchange-Organization-Network-Message-Id: [redacted]
X-MS-Exchange-Organization-AVStamp-Enterprise: 1.0
这封电子邮件 header 是对上述电子邮件的回复。在 MailKit 中获取时，它没有文本Body，而是有一个 HtmlBody:
Received: from [ExchangeHost] ([ExchangeIP]) by [ExchangeHost]
([ExchangeIP]) with Microsoft SMTP Server (TLS) id 15.0.1320.4 via Mailbox
Transport; Mon, 10 Aug 2020 11:27:16 -0400
Received: from [ExchangeHost] ([ExchangeIP]) by [ExchangeHost]
([ExchangeIP]) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Mon, 10 Aug 2020
11:27:16 -0400
Received: from [SenderHost] ([SenderIP]) by
[ExchangeHost] ([ExhcangeIP]) with Microsoft SMTP Server id 15.0.1320.4
via Frontend Transport; Mon, 10 Aug 2020 11:27:15 -0400
IronPort-SDR: [redacted]
X-IronPort-AV: [redacted]
From: <[SenderAddr2]>
To: <[MyExchangeAddr]>, <[SenderAddr1]>
Subject: RE: [redacted]
Thread-topic: [redacted]
Thread-index: [redacted]
Date: Mon, 10 Aug 2020 15:27:07 +0000
Message-ID: <[redacted]>
References: <[redacted]>
In-Reply-To: <[redacted]>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-ms-exchange-messagesentrepresentingtype: 1
x-ms-exchange-transport-fromentityheader: Hosted
x-tm-snts-smtp: [redacted]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Return-Path: [SenderAddr2]
X-GFI-SMTP-Submission: 1
X-GFI-SMTP-HelloDomain: [SenderHost]
X-GFI-SMTP-RemoteIP: [SenderIP]
X-MS-Exchange-Organization-Network-Message-Id: [redacted]
X-MS-Exchange-Organization-AVStamp-Enterprise: 1.0
X-Auto-Response-Suppress: DR, OOF, AutoReply
X-MS-Exchange-Organization-AuthSource: [ExchangeHost]
X-MS-Exchange-Organization-AuthAs: Anonymous
后一封来自MailKit的邮件的HTMLBody：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Exchange Server">
<!-- converted from text -->
<style><!-- .EmailQuote { margin-left: 1pt; padding-left: 4pt; border-left: #800000 2px solid; } --></style>
</head>
<body>
<!-- the stuff that should be in plain text, formatted as HTML -->
</body>
</html>
在 Outlook 中，后一封电子邮件采用纯文本格式，就像其 header 的 Content-Type 指定的那样。由于邮件在 Outlook 中的格式正确，我的问题是：
- 在使用 MailKit 时我需要做些什么来防止这种转换发生吗？
- （我怀疑更有可能）我的系统管理员是否需要为 Exchange 帐户设置一些选项以防止发生这种自动转换？
我已经阅读了 here 和其他主题中的解决方案，但是其中 none 似乎今天仍然适用，因为关于这个主题的任何问题都已经有将近十年的历史了。
- IMAP（以及 MailKit）无法指定不进行任何转换，它只是假定不会发生任何转换，因为其他 IMAP 服务器不会这样做。
- 大概 Exchange 2003 的相同选项也存在于 2013 年。
因此，我发现 Exchange 出现问题的原因是因为我复制了收到的电子邮件以进行测试。尽管重复的电子邮件具有相同的 headers，但在使用 MailKit 获取时，Exchange 仅将复制的电子邮件转换为 HTML。然而，原件正在按预期取回。为了将来参考任何人，如果您希望它保留其纯文本，请不要 copy/paste 在您的收件箱中发送电子邮件！
在使用 IMAP 连接到 Microsoft Exchange 2013 帐户时，我正在使用 MailKit v2.8 解析电子邮件中的数据。发送到我的 Exchange 收件箱的 body 封邮件在 100% 的时间里都是“text/plain”。此过程对于新电子邮件完全正常（并且已经投入生产使用了几个月），但是这些电子邮件的 replies/forwards 可能在提取时由 Exchange 转换为 HTML。服务器上回复邮件的 header 仍然指定消息 body 是“text/plain”。 Outlook 也以纯文本显示响应，但出于某种原因，当我尝试使用 MailKit 获取消息摘要的 TextPart 时，它返回 null。
MailKit 邮件获取代码：
using var imap = new ImapClient {
ServerCertificateValidationCallback = (mySender, cert, chain, sslPolicyErrors) => { return true; },
CheckCertificateRevocation = false
};
try {
await imap.ConnectAsync(_config.ImapServer, _config.ImapPort, SecureSocketOptions.SslOnConnect);
imap.AuthenticationMechanisms.Remove("XOAUTH2");
await imap.AuthenticateAsync(_config.ImapUsername, _config.ImapPassword);
var inbox = imap.Inbox;
if (!string.IsNullOrWhiteSpace(_config.Inbox)) { // set inbox to subfolder for devenv
inbox = await imap.Inbox.GetSubfolderAsync(_config.Inbox);
}
await inbox.OpenAsync(FolderAccess.ReadWrite);
var uIds = await inbox.SearchAsync(SearchQuery.All);
var msgs = await inbox.FetchAsync(uIds, MessageSummaryItems.UniqueId | MessageSummaryItems.BodyStructure | MessageSummaryItems.Envelope);
foreach (var msg in msgs) {
var bodyPart = msg.TextBody; // <-- this returns null for the latter email, but contains a body for the former
var body = await inbox.GetBodyPartAsync(msg.UniqueId, bodyPart) as TextPart;
if (_config.SendingAddresses.Any(msg.Envelope.From.Mailboxes.Select(a => a.Address).Contains)) { // sent from valid address
// parse and process email body
} else {
// discard and expunge
}
}
} catch (Exception e) {
// log exception
}
为简洁起见，这里有一个例子。使用 MailKit 获取时，此电子邮件包含文本Body：
Received: from [ExchangeHost] ([ExchangeIP]) by [ExchangeHost]
([ExchangeIP]) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Thu, 6 Aug 2020
17:30:12 -0400
Received: from [SenderHost] ([SenderIP]) by
[ExchangeHost] ([ExchangeIP]) with Microsoft SMTP Server id 15.0.1320.4
via Frontend Transport; Thu, 6 Aug 2020 17:30:11 -0400
IronPort-SDR: [redacted]
X-IronPort-AV: [redacted]
X-AuditID: [redacted]
MIME-Version: 1.0
Message-ID: <[redacted]>
From: <[SenderAddr1]>
To: <[MyExchangeAddr]>
Date: Thu, 6 Aug 2020 14:30:03 -0700
Subject: [redacted]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
Return-Path: [SenderAddr1]
X-MS-Exchange-Organization-AuthSource: [ExchangeHost]
X-MS-Exchange-Organization-AuthAs: Anonymous
X-GFI-SMTP-Submission: 1
X-GFI-SMTP-HelloDomain: [SenderHost]
X-GFI-SMTP-RemoteIP: [SenderIP]
X-MS-Exchange-Organization-Network-Message-Id: [redacted]
X-MS-Exchange-Organization-AVStamp-Enterprise: 1.0
这封电子邮件 header 是对上述电子邮件的回复。在 MailKit 中获取时，它没有文本Body，而是有一个 HtmlBody:
Received: from [ExchangeHost] ([ExchangeIP]) by [ExchangeHost]
([ExchangeIP]) with Microsoft SMTP Server (TLS) id 15.0.1320.4 via Mailbox
Transport; Mon, 10 Aug 2020 11:27:16 -0400
Received: from [ExchangeHost] ([ExchangeIP]) by [ExchangeHost]
([ExchangeIP]) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Mon, 10 Aug 2020
11:27:16 -0400
Received: from [SenderHost] ([SenderIP]) by
[ExchangeHost] ([ExhcangeIP]) with Microsoft SMTP Server id 15.0.1320.4
via Frontend Transport; Mon, 10 Aug 2020 11:27:15 -0400
IronPort-SDR: [redacted]
X-IronPort-AV: [redacted]
From: <[SenderAddr2]>
To: <[MyExchangeAddr]>, <[SenderAddr1]>
Subject: RE: [redacted]
Thread-topic: [redacted]
Thread-index: [redacted]
Date: Mon, 10 Aug 2020 15:27:07 +0000
Message-ID: <[redacted]>
References: <[redacted]>
In-Reply-To: <[redacted]>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-ms-exchange-messagesentrepresentingtype: 1
x-ms-exchange-transport-fromentityheader: Hosted
x-tm-snts-smtp: [redacted]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Return-Path: [SenderAddr2]
X-GFI-SMTP-Submission: 1
X-GFI-SMTP-HelloDomain: [SenderHost]
X-GFI-SMTP-RemoteIP: [SenderIP]
X-MS-Exchange-Organization-Network-Message-Id: [redacted]
X-MS-Exchange-Organization-AVStamp-Enterprise: 1.0
X-Auto-Response-Suppress: DR, OOF, AutoReply
X-MS-Exchange-Organization-AuthSource: [ExchangeHost]
X-MS-Exchange-Organization-AuthAs: Anonymous
后一封来自MailKit的邮件的HTMLBody：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Exchange Server">
<!-- converted from text -->
<style><!-- .EmailQuote { margin-left: 1pt; padding-left: 4pt; border-left: #800000 2px solid; } --></style>
</head>
<body>
<!-- the stuff that should be in plain text, formatted as HTML -->
</body>
</html>
在 Outlook 中，后一封电子邮件采用纯文本格式，就像其 header 的 Content-Type 指定的那样。由于邮件在 Outlook 中的格式正确，我的问题是：
- 在使用 MailKit 时我需要做些什么来防止这种转换发生吗？
- （我怀疑更有可能）我的系统管理员是否需要为 Exchange 帐户设置一些选项以防止发生这种自动转换？
我已经阅读了 here 和其他主题中的解决方案，但是其中 none 似乎今天仍然适用，因为关于这个主题的任何问题都已经有将近十年的历史了。
- IMAP（以及 MailKit）无法指定不进行任何转换，它只是假定不会发生任何转换，因为其他 IMAP 服务器不会这样做。
- 大概 Exchange 2003 的相同选项也存在于 2013 年。
因此，我发现 Exchange 出现问题的原因是因为我复制了收到的电子邮件以进行测试。尽管重复的电子邮件具有相同的 headers，但在使用 MailKit 获取时，Exchange 仅将复制的电子邮件转换为 HTML。然而，原件正在按预期取回。为了将来参考任何人，如果您希望它保留其纯文本，请不要 copy/paste 在您的收件箱中发送电子邮件！