diff --git a/api/src/Mail.php b/api/src/Mail.php
index 09150f2d2d..af11f64290 100644
--- a/api/src/Mail.php
+++ b/api/src/Mail.php
@@ -6209,7 +6209,7 @@ class Mail
 	 * @param string _body body part of message, only used if _header is NO resource
 	 * @param string _flags = '\\Recent'the imap flags to set for the saved message
 	 *
-	 * @return the id of the message appended or exception
+	 * @return int id of the message appended or exception
 	 * @throws Exception\WrongUserinput
 	 */
 	function appendMessage($_folderName, $_header, $_body, $_flags='\\Recent')
diff --git a/doc/REST-CalDAV-CardDAV/Mail.md b/doc/REST-CalDAV-CardDAV/Mail.md
index 626c2b3cf2..ad6f29c831 100644
--- a/doc/REST-CalDAV-CardDAV/Mail.md
+++ b/doc/REST-CalDAV-CardDAV/Mail.md
@@ -41,6 +41,7 @@ The content of the POST request is a JSON encoded object with following attribut
 - ```subject```: string with subject
 - ```body```: string plain text body (optional)
 - ```bodyHtml```: string with html body (optional)
+- ```replyEml```: string returned from uploaded eml file to reply to (optional)
 - ```attachments```: array of strings returned from uploaded attachments (see below) or VFS path ```["/mail/attachments/<token>", "/home/<user>/<filename>", ...]```
 - ```attachmentType```: one of the following strings (optional, default "attach")
   - "attach" send as attachment
diff --git a/mail/inc/class.mail_compose.inc.php b/mail/inc/class.mail_compose.inc.php
index a6abd6b0b2..931610252d 100644
--- a/mail/inc/class.mail_compose.inc.php
+++ b/mail/inc/class.mail_compose.inc.php
@@ -1014,9 +1014,31 @@ class mail_compose
 						$_content[$name]=$content[$name]=$_REQUEST['preset'][$name];
 					}
 					//skip if already processed by "preset Routines"
-					if ($alreadyProcessed[$name]) continue;
-					//error_log(__METHOD__.__LINE__.':'.$name.'->'. $_REQUEST['preset'][$name]);
-					if (!empty($_REQUEST['preset'][$name])) $content[$name] = $_REQUEST['preset'][$name];
+					if ($alreadyProcessed[$name] || empty($_REQUEST['preset'][$name]))
+					{
+						continue;
+					}
+					if ($name === 'body' && !empty($content['body']))
+					{
+						// if preset body has different mimeType the (reply-)body --> convert all to html
+						if ($content['mimeType'] !== $_REQUEST['preset']['mimeType'])
+						{
+							if ($_REQUEST['preset']['mimeType'] === 'plain')
+							{
+								$_REQUEST['preset']['body'] = '<p>'.nl2br($_REQUEST['preset']['body'])."</p>\n";
+							}
+							else
+							{
+								$content['body'] = '<pre>'.$content['body']."</pre>\n";
+							}
+							$content['mimeType'] = $_REQUEST['preset']['mimeType'] = 'html';
+						}
+						$content['body'] = $_REQUEST['preset']['body'].$content['body'];
+					}
+					else
+					{
+						$content[$name] = $_REQUEST['preset'][$name];
+					}
 				}
 				// if we preset the body, we always want the signature below (independent of user preference for replay or forward!)
 				if (!empty($_REQUEST['preset']['body']))
diff --git a/mail/src/ApiHandler.php b/mail/src/ApiHandler.php
index 8d042dc3bc..ff327f6d11 100644
--- a/mail/src/ApiHandler.php
+++ b/mail/src/ApiHandler.php
@@ -75,7 +75,7 @@ class ApiHandler extends Api\CalDAV\Handler
 			}
 			elseif (preg_match('#^/mail(/(\d+))?(/compose)?#', $path, $matches))
 			{
-				$ident_id = $matches[2] ?? self::defaultIdentity($user);
+				$ident_id = $matches[2] ?? null ?: self::defaultIdentity($user);
 				$do_compose = (bool)($matches[3] ?? false);
 				if (!($data = json_decode($options['content'], true)))
 				{
@@ -83,7 +83,33 @@ class ApiHandler extends Api\CalDAV\Handler
 				}
 				// ToDo: check required attributes
 
-				$preset = array_filter(array_intersect_key($data, array_flip(['to', 'cc', 'bcc', 'replyto', 'subject', 'priority']))+[
+				$params = [];
+
+				// should we reply to an eml file
+				if (!empty($data['replyEml']))
+				{
+					if (preg_match('#^/mail/attachments/(([^/]+)--[^/.-]{6,})$#', $data['replyEml'], $matches) &&
+						file_exists($eml=$GLOBALS['egw_info']['server']['temp_dir'].'/attach--'.$matches[1]))
+					{
+						// import mail into drafts folder
+						$acc_id = Api\Mail\Account::read_identity($ident_id)['acc_id'];
+						$mail = Api\Mail::getInstance(false, $acc_id);
+						$folder = $mail->getDraftFolder();
+						$mailer = new Api\Mailer();
+						$mail->parseFileIntoMailObject($mailer, $eml);
+						$mail->openConnection();
+						$uid = $mail->appendMessage($folder, $mailer->getRaw(), null, '\\Seen');
+						// and generate row-id from it to pass as reply_id to compose
+						$params['reply_id'] = \mail_ui::generateRowID($acc_id, $folder, $uid, true);
+						$params['from'] = 'reply';
+					}
+					else
+					{
+						throw new \Exception("Reply message eml '{$data['reply_eml']}' NOT found", 400);
+					}
+				}
+
+				$preset = array_filter(array_intersect_key($data, array_flip(['to', 'cc', 'bcc', 'replyto', 'subject', 'priority', 'reply_id']))+[
 					'body' => $data['bodyHtml'] ?? null ?: $data['body'] ?? '',
 					'mimeType' => !empty($data['bodyHtml']) ? 'html' : 'plain',
 					'identity' => $ident_id,
@@ -99,7 +125,7 @@ class ApiHandler extends Api\CalDAV\Handler
 						throw new \Exception("User '$account_lid' (#$user) is NOT online", 404);
 					}
 					$push = new Api\Json\Push($user);
-					$push->call('egw.open', '', 'mail', 'add', ['preset' => $preset], '_blank', 'mail');
+					$push->call('egw.open', '', 'mail', 'add', $params+['preset' => $preset], '_blank', 'mail');
 					echo json_encode([
 						'status' => 200,
 						'message' => 'Request to open compose window sent',
@@ -107,7 +133,7 @@ class ApiHandler extends Api\CalDAV\Handler
 					], self::JSON_RESPONSE_OPTIONS);
 					return true;
 				}
-				$acc_id = Api\Mail\Account::read_identity($ident_id)['acc_id'];
+				$acc_id = $acc_id ?? Api\Mail\Account::read_identity($ident_id)['acc_id'];
 				$mail_account = Api\Mail\Account::read($acc_id);
 				// check if the mail-account requires a user-context / password and then just send the mail with an smtp-only account NOT saving to Sent folder
 				if (empty($mail_account->acc_imap_password) || $mail_account->acc_smtp_auth_session && empty($mail_account->acc_smtp_password))