eMClient keeps crashing because of large attachment

eMClient keeps crashing. I sent a too large attachment, 67 MGS. I get a popup message letting me know that the file was not sent and is in the Outbox, however, when I look in the Outbox, there is nothing there. Every few hours, em client crashes and I get a box with a huge error message. I am on a macbook pro, by the way. Is there a way to resolve this problem?

thank you

Disconnect from the Internet.

Open eM Client.

Choose Preferences > General > General > Show Local Folders.

Click on Save & Close.

Delete the message in the Local Folder Outbox.

Reconnect to the Internet.