In Mary's personal letters....

[BettyO]

Victorian convention was extremely strict in some instances. There were actually some couples who, throughout their married life, who referred to themselves as Mr. and Mrs; i.e. Mr. Jones and Mrs. Jones when addressing themselves. There were also those who simply did give a bit of casualness to their addresses - either in person or by letter. I've seen letters with Dear John or Dear Sally in the salutations as well. I guess it was simply how "genteel" or well bred one wanted to appear. Being a "lady" or "gentleman" was the ultimate in "Cool" in the 19th Century - so folk would want to appear well bred. Likewise, Mrs. Lincoln would want to appear very high toned - so therefore she apparently wrote formally even to close acquaintances.