Reply arrow missing on replied-to emails

Hey Abstractman23,

We'd recommend reviewing this article for more information on replying in Mac Mail: Reply to, forward, or follow up on emails in Mail on Mac - Apple Support

"Reply to or forward emails

1. In the Mail app  on your Mac, select a message in the message list.
2. To include just a portion of the original message in your reply, select the text to include.
3. If you select the top message in a conversation, all of the messages in the conversation are selected.
4. Move the pointer over the message header, then click one of the following buttons:

• Reply  to reply to just the sender.
• Reply All  to reply to the sender and the other recipients.
• Forward  to choose new recipients.

1. You can add or remove recipients as needed.
2. Add your text.
3. If you included the original message, vertical bars (called quotation bars) may appear next to it.
4. You can make your text appear as quotations:

• Add quotation bars to your text: Choose Format > Quote Level > Increase or Format > Quote Level > Decrease. This also changes the quote level at which selected text appears.
• Paste text as quoted text: Choose Edit > Paste as Quotation. 

1. If the original message contains attachments, decide whether to include them: 

• Include attachments: Click the Include Attachment button  in the toolbar of the message window or choose Edit > Attachments > Include Original Attachments in Reply.
• Exclude attachments: Click the Exclude Attachment button  in the toolbar of the message window or choose Message > Remove Attachments.
• Choose attachments settings for all replies: Choose Edit > Include Attachments With Replies, then select an option.

1. When you’re ready, click the Send button . 

If you prefer to always omit the original message from your replies, choose Mail > Settings, click Composing, then deselect “Quote the text of the original message.”"

If that doesn't help, we'd recommend contacting Apple Support for assistance here: Get Support

Thanks!